1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
|
<!DOCTYPE html>
<html lang="en-US" id="hacks-mozilla-org">
<head>
<meta name="viewport" content="width=device-width"/>
<meta charset="UTF-8"/>
<!-- OpenGraph metadata -->
<meta property="og:site_name" content="Mozilla Hacks – the Web developer blog"/>
<meta property="og:title" content="This API is so Fetching!"/>
<meta property="og:url" content="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/"/>
<meta property="og:description" content="For more than a decade the Web has used XMLHttpRequest (XHR) to achieve asynchronous requests in JavaScript. While very useful, XHR is not a very ..."/>
<!--[if IE]>
<meta name="MSSmartTagsPreventParsing" content="true"/>
<meta http-equiv="imagetoolbar" content="no"/>
<meta http-equiv="X-UA-Compatible" content="IE=Edge"/>
<script src="https://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<link rel="shortcut icon" type="image/ico" href="https://hacks.mozilla.org/wp-content/themes/Hacks2013/favicon.ico"/>
<link rel="home" href="/"/>
<link rel="copyright" href="#copyright"/>
<link rel="stylesheet" type="text/css" media="screen,projection" href="https://hacks.mozilla.org/wp-content/themes/Hacks2013/style.css"/>
<link rel="stylesheet" type="text/css" media="print,handheld" href="https://hacks.mozilla.org/wp-content/themes/Hacks2013/css/print.css"/>
<link rel="stylesheet" type="text/css" media="all" href="https://www.mozilla.org/tabzilla/media/css/tabzilla.css"/>
<link rel="stylesheet" type="text/css" media="all" href="https://hacks.mozilla.org/wp-content/themes/Hacks2013/css/socialshare.css"/>
<link rel="alternate" type="application/rss+xml" title="Mozilla Hacks – the Web developer blog RSS Feed"
href="https://hacks.mozilla.org/feed/"/>
<link rel="pingback" href="https://hacks.mozilla.org/xmlrpc.php"/>
<link rel="canonical" href="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/"/>
<!--[if lte IE 7]>
<link rel="stylesheet" type="text/css" media="all" href="https://hacks.mozilla.org/wp-content/themes/Hacks2013/css/ie7.css"
/>
<![endif]-->
<!--[if lte IE 6]>
<link rel="stylesheet" type="text/css" media="all" href="https://hacks.mozilla.org/wp-content/themes/Hacks2013/css/ie6.css"
/>
<![endif]-->
<title>This API is so Fetching! ✩ Mozilla Hacks – the Web developer blog</title>
<script
type="text/javascript">window.hacks = {}; // http://cfsimplicity.com/61/removing-analytics-clutter-from-campaign-urls
var removeUtms = function(){ var l = window.location; if( l.hash.indexOf(
"utm" ) != -1 ){ var anchor = l.hash.match(/#(?!utm)[^&]+/); anchor = anchor?
anchor[0]: ''; if(!anchor && window.history.replaceState){ history.replaceState({},'',
l.pathname + l.search); } else { l.hash = anchor; } }; }; var _gaq = _gaq
|| []; _gaq.push(['_setAccount', 'UA-35433268-8'], ['_setAllowAnchor',
true]); _gaq.push (['_gat._anonymizeIp']); _gaq.push(['_trackPageview']);
_gaq.push( removeUtms ); (function(d, k) { var ga = d.createElement(k);
ga.type = 'text/javascript'; ga.async = true; ga.src = 'https://ssl.google-analytics.com/ga.js';
var s = d.getElementsByTagName(k)[0]; s.parentNode.insertBefore(ga, s);
})(document, 'script');</script>
<link rel="alternate" type="application/rss+xml"
title="Mozilla Hacks - the Web developer blog » This API is so Fetching! Comments Feed"
href="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/feed/"/>
<link rel="stylesheet" id="wp-syntax-css-css" href="https://hacks.mozilla.org/wp-content/plugins/wp-syntax/css/wp-syntax.css?ver=1.0"
type="text/css" media="all"/>
<script type="text/javascript" src="https://hacks.mozilla.org/wp-includes/js/jquery/jquery.js?ver=1.11.1"></script>
<script type="text/javascript" src="https://hacks.mozilla.org/wp-includes/js/jquery/jquery-migrate.min.js?ver=1.2.1"></script>
<script type="text/javascript" src="https://hacks.mozilla.org/wp-content/themes/Hacks2013/js/fc-checkcomment.js?ver=4.1"></script>
<script type="text/javascript" src="https://hacks.mozilla.org/wp-content/themes/Hacks2013/js/analytics.js?ver=4.1"></script>
<script type="text/javascript" src="https://hacks.mozilla.org/wp-content/themes/Hacks2013/js/socialshare.min.js?ver=4.1"></script>
<link rel="EditURI" type="application/rsd+xml" title="RSD" href="https://hacks.mozilla.org/xmlrpc.php?rsd"/>
<link rel="wlwmanifest" type="application/wlwmanifest+xml" href="https://hacks.mozilla.org/wp-includes/wlwmanifest.xml"/>
<link rel="prev" title="Ruby support in Firefox Developer Edition 38"
href="https://hacks.mozilla.org/2015/03/ruby-support-in-firefox-developer-edition-38/"/>
<link rel="next" title="Optimising SVG images" href="https://hacks.mozilla.org/2015/03/optimising-svg-images/"/>
<link rel="canonical" href="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/"/>
<link rel="shortlink" href="https://hacks.mozilla.org/?p=28260"/>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-36116321-4']);
_gaq.push(['_trackPageview']);
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
</script>
</head>
<body class="single single-post postid-28260 single-format-standard">
<div id="outer-wrapper">
<ul id="nav-access" role="navigation">
<li><a href="#content-main">Skip to content</a>
</li>
</ul>
<header id="branding">
<h4 id="logo">hacks.mozilla.org <a href="https://hacks.mozilla.org" title="Go to the home page">Home</a></h4>
<form id="fm-search" method="get" action="https://hacks.mozilla.org/"
role="search">
<p>
<input type="search" placeholder="Search hacks.mozilla.org" value="" name="s"
id="s"/>
<button type="submit">Go</button>
</p>
</form>
<nav id="nav-main">
<ul role="navigation">
<li><a href="https://hacks.mozilla.org">Home</a>
</li>
<li><a href="https://hacks.mozilla.org/articles/">Articles</a>
</li>
<li><a href="https://hacks.mozilla.org/demos/">Demos</a>
</li>
<li><a href="https://hacks.mozilla.org/about/">About</a>
</li>
</ul>
</nav> <a href="#" id="tabzilla">Mozilla</a>
</header>
<!-- /#branding -->
<div id="content">
<div id="content-head">
<ul class="nav-crumbs">
<li><a href="https://hacks.mozilla.org" title="Go to the home page">Home</a>
</li>
<li><a href="https://hacks.mozilla.org/articles/">Articles</a>
</li>
</ul>
<h1 class="page-title">This API is so Fetching!</h1>
<ul class="nav-paging">
<li class="prev"><a href="https://hacks.mozilla.org/2015/03/ruby-support-in-firefox-developer-edition-38/"
rel="prev">Older Article</a>
</li>
<li class="next"><a href="https://hacks.mozilla.org/2015/03/optimising-svg-images/" rel="next">Newer Article</a>
</li>
</ul>
<div id="content-bar" class="single">
<div class="entry-meta">
<p class="entry-posted">on <abbr class="published" title="2015-03-10T08:05:41-07:00">March 10, 2015</abbr>
by
<a
href="https://hacks.mozilla.org/author/nmarathemozilla-com/" title="Posts by Nikhil Marathe"
class="url fn" rel="author">Nikhil Marathe</a>
</p>
<p class="entry-cat">in <a href="https://hacks.mozilla.org/category/featured/" rel="category tag">Featured Article</a>
<a
href="https://hacks.mozilla.org/category/serviceworkers/" rel="category tag">ServiceWorkers</a> <a href="https://hacks.mozilla.org/category/web-workers/"
rel="category tag">Web Workers</a> <a href="https://hacks.mozilla.org/category/webapi/"
rel="category tag">WebAPI</a>
</p>
</div>
<ul class="entry-extra">
<li class="comments"> <a href="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/#comments">2 comments</a>
</li>
<li class="share">
<div class="socialshare" data-type="small-bubbles"></div>
</li>
</ul>
</div>
</div>
<!-- /#content-head -->
<main id="content-main" class="hfeed">
<article class="post" role="article">
<p>For more than a decade the Web has used XMLHttpRequest (XHR) to achieve
asynchronous requests in JavaScript. While very useful, XHR is not a very
nice API. It suffers from lack of separation of concerns. The input, output
and state are all managed by interacting with one object, and state is
tracked using events. Also, the event-based model doesn’t play well with
JavaScript’s recent focus on Promise- and generator-based asynchronous
programming.</p>
<p>The <a href="https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API">Fetch API</a> intends
to fix most of these problems. It does this by introducing the same primitives
to JS that are used in the HTTP protocol. In addition, it introduces a
utility function <code>fetch()</code> that succinctly captures the intention
of retrieving a resource from the network.</p>
<p>The <a href="https://fetch.spec.whatwg.org">Fetch specification</a>, which
defines the API, nails down the semantics of a user agent fetching a resource.
This, combined with ServiceWorkers, is an attempt to:</p>
<ol>
<li>Improve the offline experience.</li>
<li>Expose the building blocks of the Web to the platform as part of the
<a
href="https://extensiblewebmanifesto.org/">extensible web movement</a>.</li>
</ol>
<p>As of this writing, the Fetch API is available in Firefox 39 (currently
Nightly) and Chrome 42 (currently dev). Github has a <a href="https://github.com/github/fetch">Fetch polyfill</a>.</p>
<h2>Feature detection</h2>
<p>Fetch API support can be detected by checking for <code>Headers</code>,<code>Request</code>, <code>Response</code> or <code>fetch</code> on
the <code>window</code> or <code>worker</code> scope.</p>
<h2>Simple fetching</h2>
<p>The most useful, high-level part of the Fetch API is the <code>fetch()</code> function.
In its simplest form it takes a URL and returns a promise that resolves
to the response. The response is captured as a <code>Response</code> object.</p>
<div
class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">fetch<span style="color: #009900;">(</span><span style="color: #3366CC;">"/data.json"</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>res<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
<span style="color: #006600; font-style: italic;">// res instanceof Response == true.</span>
<span style="color: #000066; font-weight: bold;">if</span> <span style="color: #009900;">(</span>res.<span style="color: #660066;">ok</span><span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
res.<span style="color: #660066;">json</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>data<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>data.<span style="color: #660066;">entries</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span> <span style="color: #000066; font-weight: bold;">else</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Looks like the response wasn't perfect, got status"</span><span style="color: #339933;">,</span> res.<span style="color: #660066;">status</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span>
<span style="color: #009900;">}</span><span style="color: #339933;">,</span> <span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>e<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Fetch failed!"</span><span style="color: #339933;">,</span> e<span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>Submitting some parameters, it would look like this:</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">fetch<span style="color: #009900;">(</span><span style="color: #3366CC;">"http://www.example.org/submit.php"</span><span style="color: #339933;">,</span> <span style="color: #009900;">{</span>
method<span style="color: #339933;">:</span> <span style="color: #3366CC;">"POST"</span><span style="color: #339933;">,</span>
headers<span style="color: #339933;">:</span> <span style="color: #009900;">{</span>
<span style="color: #3366CC;">"Content-Type"</span><span style="color: #339933;">:</span> <span style="color: #3366CC;">"application/x-www-form-urlencoded"</span>
<span style="color: #009900;">}</span><span style="color: #339933;">,</span>
body<span style="color: #339933;">:</span> <span style="color: #3366CC;">"firstName=Nikhil&favColor=blue&password=easytoguess"</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>res<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
<span style="color: #000066; font-weight: bold;">if</span> <span style="color: #009900;">(</span>res.<span style="color: #660066;">ok</span><span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
alert<span style="color: #009900;">(</span><span style="color: #3366CC;">"Perfect! Your settings are saved."</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span> <span style="color: #000066; font-weight: bold;">else</span> <span style="color: #000066; font-weight: bold;">if</span> <span style="color: #009900;">(</span>res.<span style="color: #660066;">status</span> <span style="color: #339933;">==</span> <span style="color: #CC0000;">401</span><span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
alert<span style="color: #009900;">(</span><span style="color: #3366CC;">"Oops! You are not authorized."</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span>
<span style="color: #009900;">}</span><span style="color: #339933;">,</span> <span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>e<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
alert<span style="color: #009900;">(</span><span style="color: #3366CC;">"Error submitting form!"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>The <code>fetch()</code> function’s arguments are the same as those passed
to the
<br/>
<code>Request()</code> constructor, so you may directly pass arbitrarily
complex requests to <code>fetch()</code> as discussed below.</p>
<h2>Headers</h2>
<p>Fetch introduces 3 interfaces. These are <code>Headers</code>, <code>Request</code> and
<br/>
<code>Response</code>. They map directly to the underlying HTTP concepts,
but have
<br/>certain visibility filters in place for privacy and security reasons,
such as
<br/>supporting CORS rules and ensuring cookies aren’t readable by third parties.</p>
<p>The <a href="https://fetch.spec.whatwg.org/#headers-class">Headers interface</a> is
a simple multi-map of names to values:</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> content <span style="color: #339933;">=</span> <span style="color: #3366CC;">"Hello World"</span><span style="color: #339933;">;</span>
<span style="color: #000066; font-weight: bold;">var</span> reqHeaders <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Headers<span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
reqHeaders.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Content-Type"</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"text/plain"</span>
reqHeaders.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Content-Length"</span><span style="color: #339933;">,</span> content.<span style="color: #660066;">length</span>.<span style="color: #660066;">toString</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
reqHeaders.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"X-Custom-Header"</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"ProcessThisImmediately"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>The same can be achieved by passing an array of arrays or a JS object
literal
<br/>to the constructor:</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">reqHeaders <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Headers<span style="color: #009900;">(</span><span style="color: #009900;">{</span>
<span style="color: #3366CC;">"Content-Type"</span><span style="color: #339933;">:</span> <span style="color: #3366CC;">"text/plain"</span><span style="color: #339933;">,</span>
<span style="color: #3366CC;">"Content-Length"</span><span style="color: #339933;">:</span> content.<span style="color: #660066;">length</span>.<span style="color: #660066;">toString</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #339933;">,</span>
<span style="color: #3366CC;">"X-Custom-Header"</span><span style="color: #339933;">:</span> <span style="color: #3366CC;">"ProcessThisImmediately"</span><span style="color: #339933;">,</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>The contents can be queried and retrieved:</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>reqHeaders.<span style="color: #660066;">has</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Content-Type"</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// true</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>reqHeaders.<span style="color: #660066;">has</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Set-Cookie"</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// false</span>
reqHeaders.<span style="color: #000066; font-weight: bold;">set</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Content-Type"</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"text/html"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
reqHeaders.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"X-Custom-Header"</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"AnotherValue"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>reqHeaders.<span style="color: #000066; font-weight: bold;">get</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Content-Length"</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// 11</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>reqHeaders.<span style="color: #660066;">getAll</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"X-Custom-Header"</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// ["ProcessThisImmediately", "AnotherValue"]</span>
reqHeaders.<span style="color: #000066; font-weight: bold;">delete</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"X-Custom-Header"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>reqHeaders.<span style="color: #660066;">getAll</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"X-Custom-Header"</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// []</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>Some of these operations are only useful in ServiceWorkers, but they provide
<br/>a much nicer API to Headers.</p>
<p>Since Headers can be sent in requests, or received in responses, and have
various limitations about what information can and should be mutable, <code>Headers</code> objects
have a <strong>guard</strong> property. This is not exposed to the Web, but
it affects which mutation operations are allowed on the Headers object.
<br/>Possible values are:</p>
<ul>
<li>“none”: default.</li>
<li>“request”: guard for a Headers object obtained from a Request (<code>Request.headers</code>).</li>
<li>“request-no-cors”: guard for a Headers object obtained from a Request
created
<br/>with mode “no-cors”.</li>
<li>“response”: naturally, for Headers obtained from Response (<code>Response.headers</code>).</li>
<li>“immutable”: Mostly used for ServiceWorkers, renders a Headers object
<br/>read-only.</li>
</ul>
<p>The details of how each guard affects the behaviors of the Headers object
are
<br/>in the <a href="https://fetch.spec.whatwg.org">specification</a>. For example,
you may not append or set a “request” guarded Headers’ “Content-Length”
header. Similarly, inserting “Set-Cookie” into a Response header is not
allowed so that ServiceWorkers may not set cookies via synthesized Responses.</p>
<p>All of the Headers methods throw TypeError if <code>name</code> is not a
<a
href="https://fetch.spec.whatwg.org/#concept-header-name">valid HTTP Header name</a>. The mutation operations will throw TypeError
if there is an immutable guard. Otherwise they fail silently. For example:</p>
<div
class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> res <span style="color: #339933;">=</span> Response.<span style="color: #660066;">error</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #000066; font-weight: bold;">try</span> <span style="color: #009900;">{</span>
res.<span style="color: #660066;">headers</span>.<span style="color: #000066; font-weight: bold;">set</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Origin"</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"http://mybank.com"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span> <span style="color: #000066; font-weight: bold;">catch</span><span style="color: #009900;">(</span>e<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Cannot pretend to be a bank!"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<h2>Request</h2>
<p>The Request interface defines a request to fetch a resource over HTTP.
URL, method and headers are expected, but the Request also allows specifying
a body, a request mode, credentials and cache hints.</p>
<p>The simplest Request is of course, just a URL, as you may do to GET a
resource.</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> req <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Request<span style="color: #009900;">(</span><span style="color: #3366CC;">"/index.html"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>req.<span style="color: #660066;">method</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// "GET"</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>req.<span style="color: #660066;">url</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// "http://example.com/index.html"</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>You may also pass a Request to the <code>Request()</code> constructor to
create a copy.
<br/>(This is not the same as calling the <code>clone()</code> method, which
is covered in
<br/>the “Reading bodies” section.).</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> copy <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Request<span style="color: #009900;">(</span>req<span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>copy.<span style="color: #660066;">method</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// "GET"</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>copy.<span style="color: #660066;">url</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// "http://example.com/index.html"</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>Again, this form is probably only useful in ServiceWorkers.</p>
<p>The non-URL attributes of the <code>Request</code> can only be set by passing
initial
<br/>values as a second argument to the constructor. This argument is a dictionary.</p>
<div
class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> uploadReq <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Request<span style="color: #009900;">(</span><span style="color: #3366CC;">"/uploadImage"</span><span style="color: #339933;">,</span> <span style="color: #009900;">{</span>
method<span style="color: #339933;">:</span> <span style="color: #3366CC;">"POST"</span><span style="color: #339933;">,</span>
headers<span style="color: #339933;">:</span> <span style="color: #009900;">{</span>
<span style="color: #3366CC;">"Content-Type"</span><span style="color: #339933;">:</span> <span style="color: #3366CC;">"image/png"</span><span style="color: #339933;">,</span>
<span style="color: #009900;">}</span><span style="color: #339933;">,</span>
body<span style="color: #339933;">:</span> <span style="color: #3366CC;">"image data"</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>The Request’s mode is used to determine if cross-origin requests lead
to valid responses, and which properties on the response are readable.
Legal mode values are <code>"same-origin"</code>, <code>"no-cors"</code> (default)
and <code>"cors"</code>.</p>
<p>The <code>"same-origin"</code> mode is simple, if a request is made to another
origin with this mode set, the result is simply an error. You could use
this to ensure that
<br/>a request is always being made to your origin.</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> arbitraryUrl <span style="color: #339933;">=</span> document.<span style="color: #660066;">getElementById</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"url-input"</span><span style="color: #009900;">)</span>.<span style="color: #660066;">value</span><span style="color: #339933;">;</span>
fetch<span style="color: #009900;">(</span>arbitraryUrl<span style="color: #339933;">,</span> <span style="color: #009900;">{</span> mode<span style="color: #339933;">:</span> <span style="color: #3366CC;">"same-origin"</span> <span style="color: #009900;">}</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>res<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Response succeeded?"</span><span style="color: #339933;">,</span> res.<span style="color: #660066;">ok</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #339933;">,</span> <span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>e<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Please enter a same-origin URL!"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>The <code>"no-cors"</code> mode captures what the web platform does by default
for scripts you import from CDNs, images hosted on other domains, and so
on. First, it prevents the method from being anything other than “HEAD”,
“GET” or “POST”. Second, if any ServiceWorkers intercept these requests,
they may not add or override any headers except for <a href="https://fetch.spec.whatwg.org/#simple-header">these</a>.
Third, JavaScript may not access any properties of the resulting Response.
This ensures that ServiceWorkers do not affect the semantics of the Web
and prevents security and privacy issues that could arise from leaking
data across domains.</p>
<p><code>"cors"</code> mode is what you’ll usually use to make known cross-origin
requests to access various APIs offered by other vendors. These are expected
to adhere to
<br/>the <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS">CORS protocol</a>.
Only a <a href="https://fetch.spec.whatwg.org/#concept-filtered-response-cors">limited set</a> of
headers is exposed in the Response, but the body is readable. For example,
you could get a list of Flickr’s <a href="https://www.flickr.com/services/api/flickr.interestingness.getList.html">most interesting</a> photos
today like this:</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> u <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> URLSearchParams<span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
u.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">'method'</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">'flickr.interestingness.getList'</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
u.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">'api_key'</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">'<insert api key here>'</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
u.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">'format'</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">'json'</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
u.<span style="color: #660066;">append</span><span style="color: #009900;">(</span><span style="color: #3366CC;">'nojsoncallback'</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">'1'</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #000066; font-weight: bold;">var</span> apiCall <span style="color: #339933;">=</span> fetch<span style="color: #009900;">(</span><span style="color: #3366CC;">'https://api.flickr.com/services/rest?'</span> <span style="color: #339933;">+</span> u<span style="color: #009900;">)</span><span style="color: #339933;">;</span>
apiCall.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>response<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
<span style="color: #000066; font-weight: bold;">return</span> response.<span style="color: #660066;">json</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>json<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
<span style="color: #006600; font-style: italic;">// photo is a list of photos.</span>
<span style="color: #000066; font-weight: bold;">return</span> json.<span style="color: #660066;">photos</span>.<span style="color: #660066;">photo</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>photos<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
photos.<span style="color: #660066;">forEach</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>photo<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>photo.<span style="color: #660066;">title</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>You may not read out the “Date” header since Flickr does not allow it
via
<br/>
<code>Access-Control-Expose-Headers</code>.</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">response.<span style="color: #660066;">headers</span>.<span style="color: #000066; font-weight: bold;">get</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Date"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// null</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>The <code>credentials</code> enumeration determines if cookies for the other
domain are
<br/>sent to cross-origin requests. This is similar to XHR’s <code>withCredentials</code>
<br/>flag, but tri-valued as <code>"omit"</code> (default), <code>"same-origin"</code> and <code>"include"</code>.</p>
<p>The Request object will also give the ability to offer caching hints to
the user-agent. This is currently undergoing some <a href="https://github.com/slightlyoff/ServiceWorker/issues/585">security review</a>.
Firefox exposes the attribute, but it has no effect.</p>
<p>Requests have two read-only attributes that are relevant to ServiceWorkers
<br/>intercepting them. There is the string <code>referrer</code>, which is
set by the UA to be
<br/>the referrer of the Request. This may be an empty string. The other is
<br/>
<code>context</code> which is a rather <a href="https://fetch.spec.whatwg.org/#requestcredentials">large enumeration</a> defining
what sort of resource is being fetched. This could be “image” if the request
is from an
<img>tag in the controlled document, “worker” if it is an attempt to load a
worker script, and so on. When used with the <code>fetch()</code> function,
it is “fetch”.</p>
<h2>Response</h2>
<p><code>Response</code> instances are returned by calls to <code>fetch()</code>.
They can also be created by JS, but this is only useful in ServiceWorkers.</p>
<p>We have already seen some attributes of Response when we looked at <code>fetch()</code>.
The most obvious candidates are <code>status</code>, an integer (default
value 200) and <code>statusText</code> (default value “OK”), which correspond
to the HTTP status code and reason. The <code>ok</code> attribute is just
a shorthand for checking that <code>status</code> is in the range 200-299
inclusive.</p>
<p><code>headers</code> is the Response’s Headers object, with guard “response”.
The <code>url</code> attribute reflects the URL of the corresponding request.</p>
<p>Response also has a <code>type</code>, which is “basic”, “cors”, “default”,
“error” or
<br/>“opaque”.</p>
<ul>
<li><code>"basic"</code>: normal, same origin response, with all headers exposed
except
<br/>“Set-Cookie” and “Set-Cookie2″.</li>
<li><code>"cors"</code>: response was received from a valid cross-origin request.
<a
href="https://fetch.spec.whatwg.org/#concept-filtered-response-cors">Certain headers and the body</a>may be accessed.</li>
<li><code>"error"</code>: network error. No useful information describing
the error is available. The Response’s status is 0, headers are empty and
immutable. This is the type for a Response obtained from <code>Response.error()</code>.</li>
<li><code>"opaque"</code>: response for “no-cors” request to cross-origin
resource. <a href="https://fetch.spec.whatwg.org/#concept-filtered-response-opaque">Severely<br/>
restricted</a>
</li>
</ul>
<p>The “error” type results in the <code>fetch()</code> Promise rejecting with
TypeError.</p>
<p>There are certain attributes that are useful only in a ServiceWorker scope.
The
<br/>idiomatic way to return a Response to an intercepted request in ServiceWorkers
is:</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">addEventListener<span style="color: #009900;">(</span><span style="color: #3366CC;">'fetch'</span><span style="color: #339933;">,</span> <span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>event<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
event.<span style="color: #660066;">respondWith</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">new</span> Response<span style="color: #009900;">(</span><span style="color: #3366CC;">"Response body"</span><span style="color: #339933;">,</span> <span style="color: #009900;">{</span>
headers<span style="color: #339933;">:</span> <span style="color: #009900;">{</span> <span style="color: #3366CC;">"Content-Type"</span> <span style="color: #339933;">:</span> <span style="color: #3366CC;">"text/plain"</span> <span style="color: #009900;">}</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>As you can see, Response has a two argument constructor, where both arguments
are optional. The first argument is a body initializer, and the second
is a dictionary to set the <code>status</code>, <code>statusText</code> and <code>headers</code>.</p>
<p>The static method <code>Response.error()</code> simply returns an error
response. Similarly, <code>Response.redirect(url, status)</code> returns
a Response resulting in
<br/>a redirect to <code>url</code>.</p>
<h2>Dealing with bodies</h2>
<p>Both Requests and Responses may contain body data. We’ve been glossing
over it because of the various data types body may contain, but we will
cover it in detail now.</p>
<p>A body is an instance of any of the following types.</p>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer">ArrayBuffer</a>
</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView">ArrayBufferView</a> (Uint8Array
and friends)</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/API/Blob">Blob</a>/
<a
href="https://developer.mozilla.org/en-US/docs/Web/API/File">File</a>
</li>
<li>string</li>
<li><a href="https://url.spec.whatwg.org/#interface-urlsearchparams">URLSearchParams</a>
</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/API/FormData">FormData</a> –
currently not supported by either Gecko or Blink. Firefox expects to ship
this in version 39 along with the rest of Fetch.</li>
</ul>
<p>In addition, Request and Response both offer the following methods to
extract their body. These all return a Promise that is eventually resolved
with the actual content.</p>
<ul>
<li><code>arrayBuffer()</code>
</li>
<li><code>blob()</code>
</li>
<li><code>json()</code>
</li>
<li><code>text()</code>
</li>
<li><code>formData()</code>
</li>
</ul>
<p>This is a significant improvement over XHR in terms of ease of use of
non-text data!</p>
<p>Request bodies can be set by passing <code>body</code> parameters:</p>
<div
class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> form <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> FormData<span style="color: #009900;">(</span>document.<span style="color: #660066;">getElementById</span><span style="color: #009900;">(</span><span style="color: #3366CC;">'login-form'</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
fetch<span style="color: #009900;">(</span><span style="color: #3366CC;">"/login"</span><span style="color: #339933;">,</span> <span style="color: #009900;">{</span>
method<span style="color: #339933;">:</span> <span style="color: #3366CC;">"POST"</span><span style="color: #339933;">,</span>
body<span style="color: #339933;">:</span> form
<span style="color: #009900;">}</span><span style="color: #009900;">)</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>Responses take the first argument as the body.</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> res <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Response<span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">new</span> File<span style="color: #009900;">(</span><span style="color: #009900;">[</span><span style="color: #3366CC;">"chunk"</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"chunk"</span><span style="color: #009900;">]</span><span style="color: #339933;">,</span> <span style="color: #3366CC;">"archive.zip"</span><span style="color: #339933;">,</span>
<span style="color: #009900;">{</span> type<span style="color: #339933;">:</span> <span style="color: #3366CC;">"application/zip"</span> <span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>Both Request and Response (and by extension the <code>fetch()</code> function),
will try to intelligently <a href="https://fetch.spec.whatwg.org/#concept-bodyinit-extract">determine the content type</a>.
Request will also automatically set a “Content-Type” header if none is
set in the dictionary.</p>
<h3>Streams and cloning</h3>
<p>It is important to realise that Request and Response bodies can only be
read once! Both interfaces have a boolean attribute <code>bodyUsed</code> to
determine if it is safe to read or not.</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;"><span style="color: #000066; font-weight: bold;">var</span> res <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Response<span style="color: #009900;">(</span><span style="color: #3366CC;">"one time use"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>res.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// false</span>
res.<span style="color: #660066;">text</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>v<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>res.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// true</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>res.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// true</span>
res.<span style="color: #660066;">text</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span>.<span style="color: #000066; font-weight: bold;">catch</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>e<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span><span style="color: #3366CC;">"Tried to read already consumed Response"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<p>This decision allows easing the transition to an eventual <a href="https://streams.spec.whatwg.org/">stream-based</a> Fetch
API. The intention is to let applications consume data as it arrives, allowing
for JavaScript to deal with larger files like videos, and perform things
like compression and editing on the fly.</p>
<p>Often, you’ll want access to the body multiple times. For example, you
can use the upcoming <a href="http://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cache-objects">Cache API</a> to
store Requests and Responses for offline use, and Cache requires bodies
to be available for reading.</p>
<p>So how do you read out the body multiple times within such constraints?
The API provides a <code>clone()</code> method on the two interfaces. This
will return a clone of the object, with a ‘new’ body. <code>clone()</code> MUST
be called before the body of the corresponding object has been used. That
is, <code>clone()</code> first, read later.</p>
<div class="wp_syntax">
<table>
<tbody>
<tr>
<td class="code"><pre class="javascript" style="font-family:monospace;">addEventListener<span style="color: #009900;">(</span><span style="color: #3366CC;">'fetch'</span><span style="color: #339933;">,</span> <span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>evt<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
<span style="color: #000066; font-weight: bold;">var</span> sheep <span style="color: #339933;">=</span> <span style="color: #000066; font-weight: bold;">new</span> Response<span style="color: #009900;">(</span><span style="color: #3366CC;">"Dolly"</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>sheep.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// false</span>
<span style="color: #000066; font-weight: bold;">var</span> clone <span style="color: #339933;">=</span> sheep.<span style="color: #660066;">clone</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>clone.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// false</span>
clone.<span style="color: #660066;">text</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>sheep.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// false</span>
console.<span style="color: #660066;">log</span><span style="color: #009900;">(</span>clone.<span style="color: #660066;">bodyUsed</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> <span style="color: #006600; font-style: italic;">// true</span>
evt.<span style="color: #660066;">respondWith</span><span style="color: #009900;">(</span>cache.<span style="color: #660066;">add</span><span style="color: #009900;">(</span>sheep.<span style="color: #660066;">clone</span><span style="color: #009900;">(</span><span style="color: #009900;">)</span><span style="color: #009900;">)</span>.<span style="color: #660066;">then</span><span style="color: #009900;">(</span><span style="color: #000066; font-weight: bold;">function</span><span style="color: #009900;">(</span>e<span style="color: #009900;">)</span> <span style="color: #009900;">{</span>
<span style="color: #000066; font-weight: bold;">return</span> sheep<span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span>
<span style="color: #009900;">}</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span></pre>
</td>
</tr>
</tbody>
</table>
</div>
<h2>Future improvements</h2>
<p>Along with the transition to streams, Fetch will eventually have the ability
to abort running <code>fetch()</code>es and some way to report the progress
of a fetch. These are provided by XHR, but are a little tricky to fit in
the Promise-based nature of the Fetch API.</p>
<p>You can contribute to the evolution of this API by participating in discussions
on the <a href="https://whatwg.org/mailing-list">WHATWG mailing list</a> and
in the issues in the <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=WHATWG&component=Fetch&resolution=---">Fetch</a> and
<a
href="https://github.com/slightlyoff/ServiceWorker/issues">ServiceWorker</a>specifications.</p>
<p>For a better web!</p>
<p><em>The author would like to thank Andrea Marchesini, Anne van Kesteren and Ben<br/>
Kelly for helping with the specification and implementation.</em>
</p>
<footer class="entry-meta">
<p>Posted by <a href="https://hacks.mozilla.org/author/nmarathemozilla-com/"
title="Posts by Nikhil Marathe" class="url fn" rel="author">Nikhil Marathe</a>
on
<time
datetime="2015-03-10T08:05:41-07:00">March 10, 2015</time>at
<time datetime="PDT08:05:41-07:00">08:05</time>
</p>
<div class="share">
<div class="socialshare" data-type="small-bubbles"></div>
</div>
</footer>
</article>
<section id="comments">
<div id="comment-stream">
<header class="comments-head">
<h3>2 comments</h3>
<p class="open"><a href="#respond">Post a comment</a>
</p>
</header>
<ol id="comment-list" class="hfeed av">
<li id="comment-17303" class="comment even thread-even depth-1 hentry">
<p class="entry-title vcard"> <span class="photo"><img alt="" src="https://secure.gravatar.com/avatar/cc6f7a60f71adaa81b7bc798ebc71be1?s=48&d=https%3A%2F%2Fsecure.gravatar.com%2Favatar%2Fad516503a11cd5ca435acc9bb6523536%3Fs%3D48&r=G" class="avatar avatar-48 photo" height="48" width="48"/></span>
<cite
class="author fn">Alexander Petrov</cite> <span class="comment-meta">wrote on <a href="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/comment-page-1/#comment-17303" rel="bookmark" title="Permanent link to this comment by Alexander Petrov"><abbr class="published" title="2015-03-11">March 11th, 2015</abbr> at 02:57</a>:</span>
</p>
<blockquote class="entry-content">
<p>how do you abort a fetch?</p>
</blockquote>
<p class="comment-util"><a class="comment-reply-link" href="/2015/03/this-api-is-so-fetching/?replytocom=17303#respond"
onclick="return addComment.moveForm( "comment-17303", "17303", "respond", "28260" )"
aria-label="Reply to Alexander Petrov">Reply</a>
</p>
<ol class="children">
<li id="comment-17305" class="comment byuser comment-author-nmarathemozilla-com bypostauthor odd alt depth-2 hentry">
<p class="entry-title vcard"> <a href="http://blog.nikhilism.com" class="url" rel="nofollow external"
title="http://blog.nikhilism.com">
<span class="photo"><img alt="" src="https://secure.gravatar.com/avatar/098bc26c1d2d2b425b258cff67044ac1?s=48&d=https%3A%2F%2Fsecure.gravatar.com%2Favatar%2Fad516503a11cd5ca435acc9bb6523536%3Fs%3D48&r=G" class="avatar avatar-48 photo" height="48" width="48"/></span> <cite class="author fn">Nikhil Marathe</cite>
</a>
<span class="comment-meta">wrote on <a href="https://hacks.mozilla.org/2015/03/this-api-is-so-fetching/comment-page-1/#comment-17305" rel="bookmark" title="Permanent link to this comment by Nikhil Marathe"><abbr class="published" title="2015-03-11">March 11th, 2015</abbr> at 08:00</a>:</span>
</p>
<blockquote class="entry-content">
<p>At this point there is no way to do so. As mentioned in the future improvements
sections, there are ongoing attempts to find a nice way to plug abort()
into Promise based APIs.</p>
</blockquote>
<p class="comment-util"><a class="comment-reply-link" href="/2015/03/this-api-is-so-fetching/?replytocom=17305#respond"
onclick="return addComment.moveForm( "comment-17305", "17305", "respond", "28260" )"
aria-label="Reply to Nikhil Marathe">Reply</a>
</p>
</li>
<!-- #comment-## -->
</ol>
<!-- .children -->
</li>
<!-- #comment-## -->
</ol>
</div>
<div id="respond">
<form id="comment-form" action="https://hacks.mozilla.org/wp-comments-post.php"
method="post">
<fieldset>
<legend><span>Post Your Comment</span>
</legend>
<p id="cancel-comment-reply"><a rel="nofollow" id="cancel-comment-reply-link" href="/2015/03/this-api-is-so-fetching/#respond"
style="display:none;">Cancel Reply</a>
</p>
<ol>
<li id="cmt-name">
<label for="author">Your name <abbr title="(required)">*</abbr>
</label>
<input type="text" name="author" id="author" size="25" required="" aria-required="true"/>
</li>
<li id="cmt-email">
<label for="email">Your e-mail <abbr title="(required)">*</abbr>
</label>
<input type="email" name="email" id="email" size="25" required="" aria-required="true"/>
</li>
<li id="cmt-web">
<label for="url">Your website</label>
<input type="url" name="url" id="url" size="25"/>
</li>
<li id="cmt-ackbar">
<label for="age">Spam robots, please fill in this field. Humans should leave it blank.</label>
<input
type="text" name="age" id="age" size="4" tabindex="-1"/>
</li>
<li id="cmt-cmt">
<label for="comment">Your comment</label>
<textarea name="comment" id="comment" cols="50" rows="10"
required="required" aria-required="true"></textarea>
</li>
<li id="comment-submit">
<button name="submit" type="submit">Submit Comment</button>
<input type="hidden" name="comment_post_ID" value="28260"
id="comment_post_ID"/>
<input type="hidden" name="comment_parent" id="comment_parent" value="0"/>
<p style="display: none;">
<input type="hidden" id="akismet_comment_nonce" name="akismet_comment_nonce"
value="b601694886"/>
</p>
<!-- BEGIN: subscribe to comments reloaded -->
<p class="comment-form-subscriptions">
<label for="subscribe-reloaded">
<input style="width:30px" type="checkbox" name="subscribe-reloaded" id="subscribe-reloaded"
value="yes"/>Notify me of followup comments via e-mail. You can also <a href="https://hacks.mozilla.org/comment-subscriptions/?srp=28260&sra=s">subscribe</a> without
commenting.</label>
</p>
<!-- END: subscribe to comments reloaded -->
<p style="display: none;">
<input type="hidden" id="ak_js" name="ak_js" value="212"/>
</p>
</li>
</ol>
</fieldset>
</form>
</div>
</section>
<script>
jQuery("#comment-form").submit(function() { return fc_checkform('req'); });
</script>
</main>
<!-- /#content-main -->
<div id="content-sub">
<ul id="widgets">
<li class="widget author">
<h3>About the Author</h3>
<div class="vcard">
<h4 class="fn">
<a class="url" href="http://blog.nikhilism.com" rel="external me">Nikhil Marathe <span class="photo"><img alt="" src="https://secure.gravatar.com/avatar/098bc26c1d2d2b425b258cff67044ac1?s=48&d=https%3A%2F%2Fsecure.gravatar.com%2Favatar%2Fad516503a11cd5ca435acc9bb6523536%3Fs%3D48&r=G" class="avatar avatar-48 photo" height="48" width="48"/></span> </a></h4>
<p>Nikhil works on implementing Web APIs in Gecko. He is currently hacking
on ServiceWorkers, Fetch and parts of the Notification and Push APIs.</p>
<ul
class="author-meta">
<li><a href="http://blog.nikhilism.com" class="website" rel="me">blog.nikhilism.com</a>
</li>
</ul>
<p><a class="url" href="https://hacks.mozilla.org/author/nmarathemozilla-com/">Read more articles by Nikhil Marathe…</a>
</p>
</div>
</li>
<li class="widget categories">
<h3>Articles by Category</h3>
<ul class="cat-list" role="navigation">
<li class="cat-item cat-item-74992"><a href="https://hacks.mozilla.org/category/35-days/">35 Days</a> (45)</li>
<li
class="cat-item cat-item-75188"><a href="https://hacks.mozilla.org/category/font-face/">@font-face</a> (9)</li>
<li
class="cat-item cat-item-75450"><a href="https://hacks.mozilla.org/category/a-node-js-holiday-season/">A Node.JS Holiday Season</a> (12)</li>
<li
class="cat-item cat-item-75682"><a href="https://hacks.mozilla.org/category/abouthacks/">about:hacks</a> (2)</li>
<li
class="cat-item cat-item-50"><a href="https://hacks.mozilla.org/category/accessibility/">Accessibility</a> (1)</li>
<li
class="cat-item cat-item-119"><a href="https://hacks.mozilla.org/category/add-ons/">Add-ons</a> (16)</li>
<li
class="cat-item cat-item-86093"><a href="https://hacks.mozilla.org/category/javascript/animations/">Animations</a> (7)</li>
<li
class="cat-item cat-item-4213"><a href="https://hacks.mozilla.org/category/apps/">Apps</a> (94)</li>
<li
class="cat-item cat-item-76011"><a href="https://hacks.mozilla.org/category/ask-mdn/">Ask MDN</a> (3)</li>
<li
class="cat-item cat-item-25981"><a href="https://hacks.mozilla.org/category/asm-js/">asm.js</a> (10)</li>
<li
class="cat-item cat-item-221"><a href="https://hacks.mozilla.org/category/audio/">Audio</a> (42)</li>
<li
class="cat-item cat-item-76289"><a href="https://hacks.mozilla.org/category/bleeding-edge/">Bleeding edge</a> (12)</li>
<li
class="cat-item cat-item-76432"><a href="https://hacks.mozilla.org/category/boottogecko/">Boot to Gecko (B2G)</a> (12)</li>
<li
class="cat-item cat-item-76712"><a href="https://hacks.mozilla.org/category/brick/">Brick</a> (2)</li>
<li
class="cat-item cat-item-76814"><a href="https://hacks.mozilla.org/category/browserid-2/">BrowserID</a> (4)</li>
<li
class="cat-item cat-item-134"><a href="https://hacks.mozilla.org/category/canvas/">Canvas</a> (44)</li>
<li
class="cat-item cat-item-23095"><a href="https://hacks.mozilla.org/category/challenge/">Challenge</a> (9)</li>
<li
class="cat-item cat-item-70"><a href="https://hacks.mozilla.org/category/conferences/">Conferences</a> (36)</li>
<li
class="cat-item cat-item-176756"><a href="https://hacks.mozilla.org/category/cordova/">Cordova</a> (1)</li>
<li
class="cat-item cat-item-133"><a href="https://hacks.mozilla.org/category/css/">CSS</a> (109)</li>
<li
class="cat-item cat-item-185"><a href="https://hacks.mozilla.org/category/debugging/">Debugging</a> (11)</li>
<li
class="cat-item cat-item-19490"><a href="https://hacks.mozilla.org/category/demo/">Demo</a> (93)</li>
<li
class="cat-item cat-item-86249"><a href="https://hacks.mozilla.org/category/mdn/demo-studio/">Demo Studio</a> (11)</li>
<li
class="cat-item cat-item-76969"><a href="https://hacks.mozilla.org/category/dev-derby/">Dev Derby</a> (56)</li>
<li
class="cat-item cat-item-297"><a href="https://hacks.mozilla.org/category/developer-tools/">Developer Tools</a> (73)</li>
<li
class="cat-item cat-item-77083"><a href="https://hacks.mozilla.org/category/device-apis/">Device APIs</a> (14)</li>
<li
class="cat-item cat-item-894"><a href="https://hacks.mozilla.org/category/docs/">Docs</a> (96)</li>
<li
class="cat-item cat-item-230"><a href="https://hacks.mozilla.org/category/dom/">DOM</a> (23)</li>
<li
class="cat-item cat-item-77434"><a href="https://hacks.mozilla.org/category/drag-and-drop/">Drag and Drop</a> (10)</li>
<li
class="cat-item cat-item-817"><a href="https://hacks.mozilla.org/category/drumbeat/">Drumbeat</a> (2)</li>
<li
class="cat-item cat-item-77621"><a href="https://hacks.mozilla.org/category/evangelism-reps/">Evangelism Reps</a> (2)</li>
<li
class="cat-item cat-item-57"><a href="https://hacks.mozilla.org/category/event/">Event</a> (26)</li>
<li
class="cat-item cat-item-25569"><a href="https://hacks.mozilla.org/category/feature/">Feature</a> (46)</li>
<li
class="cat-item cat-item-7110"><a href="https://hacks.mozilla.org/category/featured/">Featured Article</a> (185)</li>
<li
class="cat-item cat-item-77870"><a href="https://hacks.mozilla.org/category/demo/featured-demo/">Featured Demo</a> (27)</li>
<li
class="cat-item cat-item-78138"><a href="https://hacks.mozilla.org/category/feedback-channels/">Feedback channels</a> (4)</li>
<li
class="cat-item cat-item-78354"><a href="https://hacks.mozilla.org/category/fileapi/">FileAPI</a> (17)</li>
<li
class="cat-item cat-item-500"><a href="https://hacks.mozilla.org/category/firebug/">Firebug</a> (16)</li>
<li
class="cat-item cat-item-30"><a href="https://hacks.mozilla.org/category/firefox/">Firefox</a> (223)</li>
<li
class="cat-item cat-item-36038"><a href="https://hacks.mozilla.org/category/firefox/firefox-aurora/">Firefox Aurora</a> (30)</li>
<li
class="cat-item cat-item-8802"><a href="https://hacks.mozilla.org/category/firefox/firefox-beta/">Firefox Beta</a> (3)</li>
<li
class="cat-item cat-item-78585"><a href="https://hacks.mozilla.org/category/firefox/firefox-development-highlights/">Firefox Development Highlights</a> (12)</li>
<li
class="cat-item cat-item-78857"><a href="https://hacks.mozilla.org/category/firefox/firefox-nightly/">Firefox Nightly</a> (10)</li>
<li
class="cat-item cat-item-24660"><a href="https://hacks.mozilla.org/category/firefox-os/">Firefox OS</a> (114)</li>
<li
class="cat-item cat-item-27876"><a href="https://hacks.mozilla.org/category/games-2/">Games</a> (40)</li>
<li
class="cat-item cat-item-79240"><a href="https://hacks.mozilla.org/category/geolocation/">Geolocation</a> (10)</li>
<li
class="cat-item cat-item-79514"><a href="https://hacks.mozilla.org/category/hackability/">hackability</a> (2)</li>
<li
class="cat-item cat-item-79853"><a href="https://hacks.mozilla.org/category/hackdays/">hackdays</a> (7)</li>
<li
class="cat-item cat-item-80032"><a href="https://hacks.mozilla.org/category/history-api/">History API</a> (1)</li>
<li
class="cat-item cat-item-254"><a href="https://hacks.mozilla.org/category/html5/">HTML5</a> (176)</li>
<li
class="cat-item cat-item-8633"><a href="https://hacks.mozilla.org/category/identity/">Identity</a> (8)</li>
<li
class="cat-item cat-item-16182"><a href="https://hacks.mozilla.org/category/images/">Images</a> (8)</li>
<li
class="cat-item cat-item-100532"><a href="https://hacks.mozilla.org/category/indexeddb/">IndexedDB</a> (16)</li>
<li
class="cat-item cat-item-453"><a href="https://hacks.mozilla.org/category/interviews/">Interviews</a> (4)</li>
<li
class="cat-item cat-item-4543"><a href="https://hacks.mozilla.org/category/jagermonkey/">JägerMonkey</a> (5)</li>
<li
class="cat-item cat-item-128"><a href="https://hacks.mozilla.org/category/javascript/">JavaScript</a> (141)</li>
<li
class="cat-item cat-item-697"><a href="https://hacks.mozilla.org/category/labs/">Labs</a> (3)</li>
<li
class="cat-item cat-item-4883"><a href="https://hacks.mozilla.org/category/mdn/learning/">Learning</a> (5)</li>
<li
class="cat-item cat-item-199"><a href="https://hacks.mozilla.org/category/localization/">Localization</a> (5)</li>
<li
class="cat-item cat-item-80317"><a href="https://hacks.mozilla.org/category/localstorage/">localStorage</a> (4)</li>
<li
class="cat-item cat-item-766"><a href="https://hacks.mozilla.org/category/mdn/">MDN</a> (82)</li>
<li
class="cat-item cat-item-80686"><a href="https://hacks.mozilla.org/category/css/media-queries/">Media Queries</a> (5)</li>
<li
class="cat-item cat-item-81062"><a href="https://hacks.mozilla.org/category/missionmozilla/">Mission:Mozilla</a> (9)</li>
<li
class="cat-item cat-item-124"><a href="https://hacks.mozilla.org/category/mobile/">Mobile</a> (44)</li>
<li
class="cat-item cat-item-5"><a href="https://hacks.mozilla.org/category/mozilla/">Mozilla</a> (32)</li>
<li
class="cat-item cat-item-81241"><a href="https://hacks.mozilla.org/category/mozilla-hacks-weekly/">Mozilla Hacks Weekly</a> (64)</li>
<li
class="cat-item cat-item-81399"><a href="https://hacks.mozilla.org/category/multi-touch/">Multi-touch</a> (7)</li>
<li
class="cat-item cat-item-58"><a href="https://hacks.mozilla.org/category/news/">News</a> (5)</li>
<li
class="cat-item cat-item-81514"><a href="https://hacks.mozilla.org/category/node-js/">Node.js</a> (21)</li>
<li
class="cat-item cat-item-20266"><a href="https://hacks.mozilla.org/category/offline/">Offline</a> (11)</li>
<li
class="cat-item cat-item-264728"><a href="https://hacks.mozilla.org/category/p2p-web/">P2P Web</a> (3)</li>
<li
class="cat-item cat-item-27786"><a href="https://hacks.mozilla.org/category/payments/">Payments</a> (7)</li>
<li
class="cat-item cat-item-81886"><a href="https://hacks.mozilla.org/category/people-of-games/">People of Games</a> (1)</li>
<li
class="cat-item cat-item-82131"><a href="https://hacks.mozilla.org/category/people-of-html5/">People of HTML5</a> (11)</li>
<li
class="cat-item cat-item-311"><a href="https://hacks.mozilla.org/category/performance/">Performance</a> (35)</li>
<li
class="cat-item cat-item-82359"><a href="https://hacks.mozilla.org/category/persona-2/">Persona</a> (3)</li>
<li
class="cat-item cat-item-82536"><a href="https://hacks.mozilla.org/category/presentation-2/">Presentation</a> (14)</li>
<li
class="cat-item cat-item-847"><a href="https://hacks.mozilla.org/category/privacy/">privacy</a> (2)</li>
<li
class="cat-item cat-item-60"><a href="https://hacks.mozilla.org/category/qa/">QA</a> (2)</li>
<li class="cat-item cat-item-538"><a href="https://hacks.mozilla.org/category/release/">Release</a> (4)</li>
<li
class="cat-item cat-item-907"><a href="https://hacks.mozilla.org/category/research/">Research</a> (5)</li>
<li
class="cat-item cat-item-3389"><a href="https://hacks.mozilla.org/category/screencast/">Screencast</a> (6)</li>
<li
class="cat-item cat-item-69"><a href="https://hacks.mozilla.org/category/security/">Security</a> (14)</li>
<li
class="cat-item cat-item-82787"><a href="https://hacks.mozilla.org/category/serviceworkers/">ServiceWorkers</a> (2)</li>
<li
class="cat-item cat-item-83024"><a href="https://hacks.mozilla.org/category/spdy/">SPDY</a> (2)</li>
<li
class="cat-item cat-item-83193"><a href="https://hacks.mozilla.org/category/sprints/">Sprints</a> (17)</li>
<li
class="cat-item cat-item-248"><a href="https://hacks.mozilla.org/category/standards/">Standards</a> (53)</li>
<li
class="cat-item cat-item-315"><a href="https://hacks.mozilla.org/category/survey/">Survey</a> (8)</li>
<li
class="cat-item cat-item-131"><a href="https://hacks.mozilla.org/category/svg/">SVG</a> (16)</li>
<li
class="cat-item cat-item-725"><a href="https://hacks.mozilla.org/category/test-day/">Test Day</a> (1)</li>
<li
class="cat-item cat-item-265"><a href="https://hacks.mozilla.org/category/testing/">Testing</a> (3)</li>
<li
class="cat-item cat-item-610"><a href="https://hacks.mozilla.org/category/tools/">Tools</a> (9)</li>
<li
class="cat-item cat-item-467"><a href="https://hacks.mozilla.org/category/tracemonkey/">TraceMonkey</a> (9)</li>
<li
class="cat-item cat-item-1"><a href="https://hacks.mozilla.org/category/uncategorized/">Uncategorized</a> (1)</li>
<li
class="cat-item cat-item-220"><a href="https://hacks.mozilla.org/category/video/">Video</a> (63)</li>
<li
class="cat-item cat-item-83360"><a href="https://hacks.mozilla.org/category/videoseries/">Videoseries</a> (11)</li>
<li
class="cat-item cat-item-83698"><a href="https://hacks.mozilla.org/category/web-components/">Web Components</a> (6)</li>
<li
class="cat-item cat-item-83947"><a href="https://hacks.mozilla.org/category/web-developer-toolbox/">Web Developer Toolbox</a> (5)</li>
<li
class="cat-item cat-item-84203"><a href="https://hacks.mozilla.org/category/web-developers/">Web Developers</a> (55)</li>
<li
class="cat-item cat-item-16188"><a href="https://hacks.mozilla.org/category/web-workers/">Web Workers</a> (4)</li>
<li
class="cat-item cat-item-84514"><a href="https://hacks.mozilla.org/category/webapi/">WebAPI</a> (25)</li>
<li
class="cat-item cat-item-19673"><a href="https://hacks.mozilla.org/category/webfwd/">WebFWD</a> (7)</li>
<li
class="cat-item cat-item-6946"><a href="https://hacks.mozilla.org/category/webgl/">WebGL</a> (39)</li>
<li
class="cat-item cat-item-84672"><a href="https://hacks.mozilla.org/category/webinars/">Webinars</a> (6)</li>
<li
class="cat-item cat-item-15881"><a href="https://hacks.mozilla.org/category/webrtc/">WebRTC</a> (33)</li>
<li
class="cat-item cat-item-84974"><a href="https://hacks.mozilla.org/category/websocket/">WebSocket</a> (9)</li>
<li
class="cat-item cat-item-85295"><a href="https://hacks.mozilla.org/category/wiki-wednesday/">Wiki Wednesday</a> (43)</li>
<li
class="cat-item cat-item-85568"><a href="https://hacks.mozilla.org/category/x-tag/">X-Tag</a> (2)</li>
<li
class="cat-item cat-item-85881"><a href="https://hacks.mozilla.org/category/xmlhttprequest/">XMLHttpRequest</a> (13)</li>
</ul>
</li>
</ul>
</div>
<!-- /#content-sub -->
</div>
<!-- /#content -->
<footer id="site-info">
<nav id="nav-legal">
<ul>
<li><a href="https://www.mozilla.org/privacy/websites/" rel="external">Privacy Policy</a>
</li>
<li><a href="https://www.mozilla.org/about/legal.html" rel="external">Legal Notices</a>
</li>
<li><a href="https://www.mozilla.org/legal/fraud-report/" rel="external">Report Trademark Abuse</a>
</li>
</ul>
</nav>
<p id="copyright">Except where otherwise noted, content on this site is licensed under the
<br/><a href="https://creativecommons.org/licenses/by-sa/3.0/" rel="license external">Creative Commons Attribution Share-Alike License v3.0</a> or
any later version.</p>
<nav id="nav-footer">
<h5>hacks.mozilla.org:</h5>
<ul role="navigation">
<li><a href="https://hacks.mozilla.org">Home</a>
</li>
<li><a href="https://hacks.mozilla.org/articles/">Articles</a>
</li>
<li><a href="https://hacks.mozilla.org/demos/">Demos</a>
</li>
<li><a href="https://hacks.mozilla.org/about/">About</a>
</li>
</ul>
</nav>
</footer>
<script src="https://www.mozilla.org/tabzilla/media/js/tabzilla.js"></script>
<script>
// <![CDATA[
jQuery(document).ready(function(){
jQuery(document.body).addClass("js");
});
// ]]>
</script>
<script type="text/javascript" src="https://blog.mozilla.org/hacks/wp-content/plugins/akismet/_inc/form.js?ver=3.0.4"></script>
<script type="text/javascript" src="https://hacks.mozilla.org/wp-includes/js/comment-reply.min.js?ver=4.1"></script>
</div>
</body>
</html>
<!-- Dynamic page generated in 0.592 seconds. -->
<!-- Cached page generated by WP-Super-Cache on 2015-03-13 03:27:44 -->
<!-- super cache -->
|
