-
Notifications
You must be signed in to change notification settings - Fork 0
/
2018-12-28-(转)深入浅出JavaScript运行进制.html
1320 lines (745 loc) · 58.8 KB
/
2018-12-28-(转)深入浅出JavaScript运行进制.html
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
<!DOCTYPE html>
<html class="theme-next mist use-motion" lang="zh-Hans">
<head>
<meta charset="UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
<meta name="theme-color" content="#222">
<script src="/lib/pace/pace.min.js?v=1.0.2"></script>
<link href="/lib/pace/pace-theme-minimal.min.css?v=1.0.2" rel="stylesheet">
<meta http-equiv="Cache-Control" content="no-transform" />
<meta http-equiv="Cache-Control" content="no-siteapp" />
<link href="/lib/fancybox/source/jquery.fancybox.css?v=2.1.5" rel="stylesheet" type="text/css" />
<link href="/lib/font-awesome/css/font-awesome.min.css?v=4.6.2" rel="stylesheet" type="text/css" />
<link href="/css/main.css?v=5.1.4" rel="stylesheet" type="text/css" />
<link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon-next.png?v=5.1.4">
<link rel="icon" type="image/png" sizes="32x32" href="/images/favicon-32x32-next.png?v=5.1.4">
<link rel="icon" type="image/png" sizes="16x16" href="/images/favicon-16x16-next.png?v=5.1.4">
<link rel="mask-icon" href="/images/logo.svg?v=5.1.4" color="#222">
<meta name="keywords" content="深入浅出 JavaScript," />
<link rel="alternate" href="/atom.xml" title="赖同学" type="application/atom+xml" />
<meta name="description" content="原文地址：深入浅出JavaScript运行机制（转）深入浅出JavaScript 运行机制读完之后有所收获，转载收藏。 一、引子本文介绍JavaScript运行机制，这一部分比较抽象，我们先从一道面试题入手： 123456console.log(1);setTimeout(function()&#123;console.log(3);&#125;,0);console.log(2);// 请问数字">
<meta name="keywords" content="深入浅出 JavaScript">
<meta property="og:type" content="article">
<meta property="og:title" content="（转）深入浅出JavaScript 运行机制">
<meta property="og:url" content="http://laibh.top/2018-12-28-(转)深入浅出JavaScript运行进制.html">
<meta property="og:site_name" content="赖同学">
<meta property="og:description" content="原文地址：深入浅出JavaScript运行机制（转）深入浅出JavaScript 运行机制读完之后有所收获，转载收藏。 一、引子本文介绍JavaScript运行机制，这一部分比较抽象，我们先从一道面试题入手： 123456console.log(1);setTimeout(function()&#123;console.log(3);&#125;,0);console.log(2);// 请问数字">
<meta property="og:locale" content="zh-Hans">
<meta property="og:image" content="http://upload-images.jianshu.io/upload_images/3174701-2dc8312f8c9de253?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240">
<meta property="og:image" content="http://upload-images.jianshu.io/upload_images/3174701-e1d19e1d2912a653?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240">
<meta property="og:image" content="https://image-static.segmentfault.com/148/271/1482713063-5bed3fa13cf7a_articlex">
<meta property="og:image" content="https://image-static.segmentfault.com/763/340/763340023-5bed97d166b3c_articlex">
<meta property="og:updated_time" content="2022-03-04T10:00:38.456Z">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="（转）深入浅出JavaScript 运行机制">
<meta name="twitter:description" content="原文地址：深入浅出JavaScript运行机制（转）深入浅出JavaScript 运行机制读完之后有所收获，转载收藏。 一、引子本文介绍JavaScript运行机制，这一部分比较抽象，我们先从一道面试题入手： 123456console.log(1);setTimeout(function()&#123;console.log(3);&#125;,0);console.log(2);// 请问数字">
<meta name="twitter:image" content="http://upload-images.jianshu.io/upload_images/3174701-2dc8312f8c9de253?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240">
<script type="text/javascript" id="hexo.configurations">
var NexT = window.NexT || {};
var CONFIG = {
root: '/',
scheme: 'Mist',
version: '5.1.4',
sidebar: {"position":"left","display":"post","offset":12,"b2t":false,"scrollpercent":true,"onmobile":false},
fancybox: true,
tabs: true,
motion: {"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}},
duoshuo: {
userId: '0',
author: '博主'
},
algolia: {
applicationID: '1YNH8Y3MP9',
apiKey: '61c189facf700193dfcbb902369ce227',
indexName: 'MyBlog',
hits: {"per_page":10},
labels: {"input_placeholder":"想要找些什么呢","hits_empty":"${query} 没有被找到，再试试","hits_stats":"在 ${time} ms 查找了${hits}个结果"}
}
};
</script>
<link rel="canonical" href="http://laibh.top/2018-12-28-(转)深入浅出JavaScript运行进制.html"/>
<title>（转）深入浅出JavaScript 运行机制 | 赖同学</title>
</head>
<body itemscope itemtype="http://schema.org/WebPage" lang="zh-Hans">
<div class="container sidebar-position-left page-post-detail">
<div class="headband"></div>
<header id="header" class="header" itemscope itemtype="http://schema.org/WPHeader">
<div class="header-inner"><div class="site-brand-wrapper">
<div class="site-meta ">
<div class="custom-logo-site-title">
<a href="/" class="brand" rel="start">
<span class="logo-line-before"><i></i></span>
<span class="site-title">赖同学</span>
<span class="logo-line-after"><i></i></span>
</a>
</div>
<h1 class="site-subtitle" itemprop="description"></h1>
</div>
<div class="site-nav-toggle">
<button>
<span class="btn-bar"></span>
<span class="btn-bar"></span>
<span class="btn-bar"></span>
</button>
</div>
</div>
<nav class="site-nav">
<ul id="menu" class="menu">
<li class="menu-item menu-item-home">
<a href="/" rel="section">
<i class="menu-item-icon fa fa-fw fa-home"></i> <br />
首页
</a>
</li>
<li class="menu-item menu-item-tags">
<a href="/tags/" rel="section">
<i class="menu-item-icon fa fa-fw fa-tags"></i> <br />
标签
</a>
</li>
<li class="menu-item menu-item-categories">
<a href="/categories/" rel="section">
<i class="menu-item-icon fa fa-fw fa-th"></i> <br />
分类
</a>
</li>
<li class="menu-item menu-item-archives">
<a href="/archives/" rel="section">
<i class="menu-item-icon fa fa-fw fa-archive"></i> <br />
归档
</a>
</li>
<li class="menu-item menu-item-sitemap">
<a href="/sitemap.xml" rel="section">
<i class="menu-item-icon fa fa-fw fa-sitemap"></i> <br />
站点地图
</a>
</li>
<li class="menu-item menu-item-guestbook">
<a href="/guestbook" rel="section">
<i class="menu-item-icon fa fa-fw fa-comment"></i> <br />
留言
</a>
</li>
<li class="menu-item menu-item-search">
<a href="javascript:;" class="popup-trigger">
<i class="menu-item-icon fa fa-search fa-fw"></i> <br />
搜索
</a>
</li>
</ul>
<div class="site-search">
<div class="algolia-popup popup search-popup">
<div class="algolia-search">
<div class="algolia-search-input-icon">
<i class="fa fa-search"></i>
</div>
<div class="algolia-search-input" id="algolia-search-input"></div>
</div>
<div class="algolia-results">
<div id="algolia-stats"></div>
<div id="algolia-hits"></div>
<div id="algolia-pagination" class="algolia-pagination"></div>
</div>
<span class="popup-btn-close">
<i class="fa fa-times-circle"></i>
</span>
</div>
</div>
</nav>
</div>
</header>
<main id="main" class="main">
<div class="main-inner">
<div class="content-wrap">
<div id="content" class="content">
<div id="posts" class="posts-expand">
<article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
<div class="post-block">
<link itemprop="mainEntityOfPage" href="http://laibh.top/2018-12-28-(转)深入浅出JavaScript运行进制.html">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="name" content="赖彬鸿">
<meta itemprop="description" content="">
<meta itemprop="image" content="/images/myPhoto.jpg">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="赖同学">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">（转）深入浅出JavaScript 运行机制</h2>
<div class="post-meta">
<span class="post-time">
<span class="post-meta-item-icon">
<i class="fa fa-calendar-o"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time title="创建于" itemprop="dateCreated datePublished" datetime="2018-12-28T16:49:15+08:00">
2018-12-28
</time>
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-calendar-check-o"></i>
</span>
<span class="post-meta-item-text">更新于:</span>
<time title="更新于" itemprop="dateModified" datetime="2022-03-04T18:00:38+08:00">
2022-03-04
</time>
</span>
<span class="post-category" >
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-folder-o"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/JavaScript/" itemprop="url" rel="index">
<span itemprop="name">JavaScript</span>
</a>
</span>
</span>
<span id="/2018-12-28-(转)深入浅出JavaScript运行进制.html" class="leancloud_visitors" data-flag-title="（转）深入浅出JavaScript 运行机制">
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">阅读次数:</span>
<span class="leancloud-visitors-count"></span>
</span>
<div class="post-wordcount">
<span class="post-meta-item-icon">
<i class="fa fa-file-word-o"></i>
</span>
<span class="post-meta-item-text">字数统计:</span>
<span title="字数统计">
2,401
</span>
</div>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h3 id="原文地址：深入浅出JavaScript运行机制"><a href="#原文地址：深入浅出JavaScript运行机制" class="headerlink" title="原文地址：深入浅出JavaScript运行机制"></a>原文地址：<a href="https://segmentfault.com/a/1190000016834449">深入浅出JavaScript运行机制</a></h3><h2 id="（转）深入浅出JavaScript-运行机制"><a href="#（转）深入浅出JavaScript-运行机制" class="headerlink" title="（转）深入浅出JavaScript 运行机制"></a>（转）深入浅出JavaScript 运行机制</h2><p>读完之后有所收获，转载收藏。</p>
<h3 id="一、引子"><a href="#一、引子" class="headerlink" title="一、引子"></a>一、引子</h3><p>本文介绍JavaScript运行机制，这一部分比较抽象，我们先从一道面试题入手：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">console</span>.log(<span class="number">1</span>);</span><br><span class="line">setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"><span class="built_in">console</span>.log(<span class="number">3</span>);</span><br><span class="line">},<span class="number">0</span>);</span><br><span class="line"><span class="built_in">console</span>.log(<span class="number">2</span>);</span><br><span class="line"><span class="comment">// 请问数字打印顺序是什么？</span></span><br></pre></td></tr></table></figure>
<p>这一题看似很简单，但如果你不了解JavaScript运行机制，很容易就答错了。题目的答案是依次输出1 2 3，如果你有疑惑，下文有详细解释。</p>
<h3 id="二、理解JS的单线程的概念"><a href="#二、理解JS的单线程的概念" class="headerlink" title="二、理解JS的单线程的概念"></a>二、理解JS的单线程的概念</h3><p>JavaScript语言的一大特点就是单线程，也就是说，<strong>同一个时间只能做一件事</strong>。那么，为什么JavaScript不能有多个线程呢？这样能提高效率啊。<br>JavaScript的单线程，与它的用途有关。作为浏览器脚本语言，JavaScript的主要用途是与用户互动，以及操作DOM。这决定了它只能是单线程，否则会带来很复杂的同步问题。比如，假定JavaScript同时有两个线程，一个线程在某个DOM节点上添加内容，另一个线程删除了这个节点，这时浏览器应该以哪个线程为准？<br>所以，为了避免复杂性，从一诞生，JavaScript就是单线程，这已经成了这门语言的核心特征，将来也不会改变。</p>
<h3 id="三、理解任务队列-消息队列"><a href="#三、理解任务队列-消息队列" class="headerlink" title="三、理解任务队列(消息队列)"></a>三、理解任务队列(消息队列)</h3><p>单线程就意味着，所有任务需要排队，前一个任务结束，才会执行后一个任务。如果前一个任务耗时很长，后一个任务就不得不一直等着。JavaScript语言的设计者意识到这个问题，将所有任务分成两种，<strong>一种是同步任务（synchronous），另一种是异步任务（asynchronous）</strong>。同步任务指的是，在主线程上排队执行的任务，只有前一个任务执行完毕，才能执行后一个任务；异步任务指的是，不进入主线程、而进入”任务队列”（task queue）的任务，只有”任务队列”通知主线程，某个异步任务可以执行了，该任务才会进入主线程执行。<strong>异步任务包括宏任务和微任务(后面会重点介绍)</strong>，接下来我们通过两个例子说明同步任务和异步任务的区别：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">console</span>.log(<span class="string">"A"</span>);</span><br><span class="line"><span class="keyword">while</span>(<span class="literal">true</span>){ }</span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"B"</span>);</span><br><span class="line"><span class="comment">// 请问最后的输出结果是什么？</span></span><br></pre></td></tr></table></figure>
<p>如果你的回答是A,恭喜你答对了，因为这是同步任务，程序由上到下执行，遇到while()死循环，下面语句就没办法执行。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">console</span>.log(<span class="string">"A"</span>);</span><br><span class="line">setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"B"</span>);</span><br><span class="line">},<span class="number">0</span>);</span><br><span class="line"><span class="keyword">while</span>(<span class="literal">true</span>){}</span><br><span class="line"><span class="comment">// 请问最后的输出结果是什么？</span></span><br></pre></td></tr></table></figure>
<p>如果你的答案是A，恭喜你现在对js运行机制已经有个粗浅的认识了！题目中的setTimeout()就是个异步任务。<strong>在所有同步任务执行完之前，任何的异步任务是不会执行的</strong>，关于这点下文还会详细说明。</p>
<h3 id="四、理解Event-Loop"><a href="#四、理解Event-Loop" class="headerlink" title="四、理解Event Loop"></a>四、理解Event Loop</h3><p><strong>异步执行的运行机制如下：</strong></p>
<ol>
<li>所有同步任务都在主线程上执行，形成一个执行栈（execution context stack）。</li>
<li>主线程之外，还存在一个”任务队列”（task queue）。只要异步任务有了运行结果，就在”任务队列”之中放置一个事件。</li>
<li>一旦”执行栈”中的所有同步任务执行完毕，系统就会读取”任务队列”，看看里面有哪些事件。那些对应的异步任务，于是结束等待状态，进入执行栈，开始执行。</li>
<li>主线程不断重复上面的第三步。</li>
</ol>
<p><strong>主线程从”任务队列”中读取事件，这个过程是循环不断的，所以整个的这种运行机制又称为Event Loop（事件循环）。只要主线程空了，就会去读取”任务队列”，这就是JavaScript的运行机制</strong>。这个过程会循环反复。以下这张图可以很好说明这点。<br><img src="http://upload-images.jianshu.io/upload_images/3174701-2dc8312f8c9de253?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="image"></p>
<h3 id="五、哪些语句会放入异步任务队列及放入时机"><a href="#五、哪些语句会放入异步任务队列及放入时机" class="headerlink" title="五、哪些语句会放入异步任务队列及放入时机"></a>五、哪些语句会放入异步任务队列及放入时机</h3><p>一般来说，有以下四种会放入异步任务队列：</p>
<ol>
<li>setTimeout和setlnterval</li>
<li>DOM事件</li>
<li>ES6中的Promise</li>
<li>Ajax异步请求</li>
</ol>
<p><strong>javascript 代码运行分两个阶段</strong>：</p>
<p><strong>1、预解析—把所有的函数定义提前，所有的变量声明提前，变量的赋值不提前</strong></p>
<p><strong>2、执行—从上到下执行（按照js运行机制）</strong></p>
<p>至于放入异步任务队列的时机，我们通过 setTimeout的例子和Ajax例子来详细说明：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">例题<span class="number">1</span></span><br><span class="line"><span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">0</span>; i < <span class="number">5</span>; i++) {</span><br><span class="line">setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{ </span><br><span class="line"> <span class="built_in">console</span>.log(i); </span><br><span class="line"> }, <span class="number">1000</span>);</span><br><span class="line">}</span><br><span class="line"><span class="comment">// 请问最后的输出结果是什么？</span></span><br></pre></td></tr></table></figure>
<p>for循环一次碰到一个 setTimeout()，<strong>并不是马上把setTimeout()拿到异步队列中，而要等到一秒后，才将其放到任务队列里面</strong>，一旦”执行栈”中的所有同步任务执行完毕（即for循环结束，此时i已经为5），系统就会读取已经存放”任务队列”的setTimeout()（有五个），于是答案是输出5个5。</p>
<p>上面也提到，<strong>在到达指定时间时，定时器就会将相应回调函数插入“任务队列”尾部。这就是“定时器（timer）”功能</strong>。</p>
<p><strong>关于定时器的重要补充</strong>：</p>
<p>定时器包括setTimeout与 setInterval 两个方法。它们的第二个参数是指定其回调函数推迟/每隔多少毫秒数后执行。</p>
<p>对于第二个参数有以下需要注意的地方：</p>
<p>当第二个参数缺省时，默认为 0；</p>
<p>当指定的值小于 4 毫秒，则增加到 4ms(4ms 是 HTML5 标准指定的，对于 2010 年及之前的浏览器则是 10ms);也就是说至少需要4毫秒，该setTimeout()拿到任务队列中。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 例题2</span></span><br><span class="line">$.ajax({</span><br><span class="line">url：“xxxxx<span class="string">",</span></span><br><span class="line"><span class="string">success:function (result){</span></span><br><span class="line"><span class="string">console.log("</span>a<span class="string">")</span></span><br><span class="line"><span class="string"> }</span></span><br><span class="line"><span class="string">})</span></span><br><span class="line"><span class="string">setTimeout(function (){</span></span><br><span class="line"><span class="string">console.log("</span>b<span class="string">")</span></span><br><span class="line"><span class="string">},100)</span></span><br><span class="line"><span class="string">setTimeout(function (){</span></span><br><span class="line"><span class="string">console.log("</span>c<span class="string">")</span></span><br><span class="line"><span class="string">})</span></span><br><span class="line"><span class="string">console.log("</span>d<span class="string">");</span></span><br></pre></td></tr></table></figure>
<p><img src="http://upload-images.jianshu.io/upload_images/3174701-e1d19e1d2912a653?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="Event Loop"></p>
<p>ajax加载完成时才会放入异步队列，至于这段时间不确定，所有有两种情况：①大于100ms,最后的结果是 d c b a ;②小于100ms,最后的结果便是d c a b。</p>
<p>六、微任务(Microtask)与宏任务(Macrotask)</p>
<p>我们上面提到异步任务分为宏任务和微任务，<strong>宏任务队列可以有多个，微任务队列只有一个</strong>。</p>
<ul>
<li>宏任务包括：<strong>script(全局任务)</strong>, setTimeout, setInterval, setImmediate, I/O, UI rendering。</li>
<li>微任务包括: new Promise().then(回调), process.nextTick, Object.observe(已废弃), MutationObserver(html5新特性)</li>
</ul>
<p><strong>当执行栈中的所有同步任务执行完毕时，是先执行宏任务还是微任务呢？</strong></p>
<ul>
<li>由于执行代码入口都是全局任务 script，而全局任务属于宏任务，所以当栈为空，同步任务任务执行完毕时，会先执行微任务队列里的任务。</li>
<li>微任务队列里的任务全部执行完毕后，会读取宏任务队列中拍最前的任务。</li>
<li>执行宏任务的过程中，遇到微任务，依次加入微任务队列。</li>
<li>栈空后，再次读取微任务队列里的任务，依次类推。</li>
</ul>
<p><img src="https://image-static.segmentfault.com/148/271/1482713063-5bed3fa13cf7a_articlex" alt="img"></p>
<p>一句话概括上面的流程图：<strong>当某个宏任务队列的中的任务全部执行完以后,会查看是否有微任务队列。如果有，先执行微任务队列中的所有任务，如果没有，就查看是否有其他宏任务队列</strong>。</p>
<p>接下来我们看两道例子来介绍上面流程：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Promise</span>.resolve().then(<span class="function"><span class="params">()</span>=></span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">'Promise1'</span>) </span><br><span class="line"> setTimeout(<span class="function"><span class="params">()</span>=></span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">'setTimeout2'</span>)</span><br><span class="line"> },<span class="number">0</span>)</span><br><span class="line">})</span><br><span class="line">setTimeout(<span class="function"><span class="params">()</span>=></span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">'setTimeout1'</span>)</span><br><span class="line"> <span class="built_in">Promise</span>.resolve().then(<span class="function"><span class="params">()</span>=></span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">'Promise2'</span>) </span><br><span class="line"> })</span><br><span class="line">},<span class="number">0</span>)</span><br></pre></td></tr></table></figure>
<p>最后输出结果是Promise1，setTimeout1，Promise2，setTimeout2</p>
<ul>
<li>一开始执行栈的同步任务执行完毕，会去查看是否有微任务队列，上题中存在(有且只有一个)，然后执行微任务队列中的所有任务输出Promise1，同时会生成一个宏任务 setTimeout2</li>
<li>然后去查看宏任务队列，宏任务 setTimeout1 在 setTimeout2 之前，先执行宏任务 setTimeout1，输出 setTimeout1</li>
<li>在执行宏任务setTimeout1时会生成微任务Promise2 ，放入微任务队列中，接着先去清空微任务队列中的所有任务，输出 Promise2</li>
<li>清空完微任务队列中的所有任务后，就又会去宏任务队列取一个，这回执行的是 setTimeout2</li>
</ul>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">console</span>.log(<span class="string">'----------------- start -----------------'</span>);</span><br><span class="line">setTimeout(<span class="function"><span class="params">()</span> =></span> {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">'setTimeout'</span>);</span><br><span class="line">}, <span class="number">0</span>)</span><br><span class="line"><span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function">(<span class="params">resolve, reject</span>) =></span>{</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">0</span>; i < <span class="number">5</span>; i++) {</span><br><span class="line"> <span class="built_in">console</span>.log(i);</span><br><span class="line"> }</span><br><span class="line"> resolve(); <span class="comment">// 修改promise实例对象的状态为成功的状态</span></span><br><span class="line">}).then(<span class="function"><span class="params">()</span> =></span> {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">'promise实例成功回调执行'</span>);</span><br><span class="line">})</span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">'----------------- end -----------------'</span>);</span><br></pre></td></tr></table></figure>
<p><img src="https://image-static.segmentfault.com/763/340/763340023-5bed97d166b3c_articlex" alt="img"></p>
<h3 id="七、题外话"><a href="#七、题外话" class="headerlink" title="七、题外话"></a>七、题外话</h3><p>如果要输出0~4，上面例题应该如何修改？</p>
<ol>
<li>将var变为let</li>
</ol>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i < <span class="number">5</span>; i++) {</span><br><span class="line">setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{ </span><br><span class="line"> <span class="built_in">console</span>.log(i);</span><br><span class="line"> }, <span class="number">1000</span>);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>2.加个立即执行函数</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">0</span>; i < <span class="number">5</span>; i++) {</span><br><span class="line">(<span class="function"><span class="keyword">function</span>(<span class="params">i</span>)</span>{</span><br><span class="line">setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{ </span><br><span class="line"> <span class="built_in">console</span>.log(i);</span><br><span class="line"> }, <span class="number">1000</span>);</span><br><span class="line">})(i)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>3.也可以通过这样加闭包</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">for</span>(<span class="keyword">var</span> i = <span class="number">1</span>;i < <span class="number">5</span>;i++){ </span><br><span class="line"> <span class="keyword">var</span> a = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{ </span><br><span class="line"> <span class="keyword">var</span> j = i; </span><br><span class="line"> setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{ </span><br><span class="line"> <span class="built_in">console</span>.log(j); </span><br><span class="line"> },<span class="number">1000</span>) </span><br><span class="line"> } </span><br><span class="line">a();</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="八、参考资料"><a href="#八、参考资料" class="headerlink" title="八、参考资料"></a>八、参考资料</h3><p><a href="http://www.ruanyifeng.com/blog/2014/10/event-loop.html">JavaScript 运行机制详解：再谈Event Loop</a></p>
<p><a href="https://github.com/JChehe/blog/blob/master/posts/%E5%85%B3%E4%BA%8EJavaScript%E5%8D%95%E7%BA%BF%E7%A8%8B%E7%9A%84%E4%B8%80%E4%BA%9B%E4%BA%8B.md">关于JavaScript单线程的一些事</a></p>
<p><a href="https://juejin.im/post/5b498d245188251b193d4059">JS事件循环机制（event loop）之宏任务/微任务</a></p>
<p><a href="https://www.jianshu.com/p/12b9f73c5a4f#">前端基础进阶（十二）：深入核心，详解事件循环机制</a></p>
<p><a href="https://mp.weixin.qq.com/s?__biz=MzAxODE2MjM1MA==&mid=2651555331&idx=1&sn=5a063db73329a9d8ea5c38d8eeb50741&chksm=802551c2b752d8d4020514337f9987cc6611ba878525c45507cbb9ceb52b92e060f50e76c48d&mpshare=1&scene=1&srcid=1115P2jpgUGueMlTaRe9UFYu#rd">事件循环机制的那些事</a></p>
</div>
<div>
<ul class="post-copyright">
<li class="post-copyright-author">
<strong>本文作者：</strong>
赖彬鸿
</li>
<li class="post-copyright-link">
<strong>本文链接：</strong>
<a href="http://laibh.top/2018-12-28-(转)深入浅出JavaScript运行进制.html" title="（转）深入浅出JavaScript 运行机制">http://laibh.top/2018-12-28-(转)深入浅出JavaScript运行进制.html</a>
</li>
<li class="post-copyright-license">
<strong>版权声明： </strong>
本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/3.0/" rel="external nofollow" target="_blank">CC BY-NC-SA 3.0</a> 许可协议。转载请注明出处！
</li>
</ul>
</div>
<footer class="post-footer">
<div class="post-tags">
<a href="/tags/深入浅出-JavaScript/" <i class="fa fa-tag"></i> 深入浅出 JavaScript</a>
</div>
<div class="post-nav">
<div class="post-nav-next post-nav-item">
<a href="/2018-12-21-NodeJs2-Part8.html" rel="next" title="Nodejs实战 —— 存储数据">
<i class="fa fa-chevron-left"></i> Nodejs实战 —— 存储数据
</a>
</div>
<span class="post-nav-divider"></span>
<div class="post-nav-prev post-nav-item">
<a href="/2019-1-07-NodeJs2-Part9.html" rel="prev" title="Nodejs实战 —— 测试 Node 程序">
Nodejs实战 —— 测试 Node 程序 <i class="fa fa-chevron-right"></i>
</a>
</div>
</div>
</footer>
</div>
</article>
<div class="post-spread">
<script>
window._bd_share_config = {
"common": {
"bdText": "",
"bdMini": "1",
"bdMiniList": false,
"bdPic": ""
},
"image": {
"viewList": ["tsina", "douban", "sqq", "qzone", "weixin", "twi", "fbook"],
"viewText": "分享到：",
"viewSize": "16"
},
"slide": {
"bdImg": "5",
"bdPos": "left",
"bdTop": "100"
}
}
</script>
<script>
with(document)0[(getElementsByTagName('head')[0]||body).appendChild(createElement('script')).src='/static/api/js/share.js?v=89860593.js?'+~(-new Date()/36e5)];;
</script>
</div>
</div>
</div>
<div class="comments" id="comments">
<div id="lv-container" data-id="city" data-uid="MTAyMC8zOTcwMy8xNjIzMA"></div>
</div>
</div>
<div class="sidebar-toggle">
<div class="sidebar-toggle-line-wrap">
<span class="sidebar-toggle-line sidebar-toggle-line-first"></span>
<span class="sidebar-toggle-line sidebar-toggle-line-middle"></span>
<span class="sidebar-toggle-line sidebar-toggle-line-last"></span>
</div>
</div>
<aside id="sidebar" class="sidebar">
<div class="sidebar-inner">
<ul class="sidebar-nav motion-element">
<li class="sidebar-nav-toc sidebar-nav-active" data-target="post-toc-wrap">
文章目录
</li>
<li class="sidebar-nav-overview" data-target="site-overview-wrap">
站点概览
</li>
</ul>
<section class="site-overview-wrap sidebar-panel">
<div class="site-overview">
<div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
<img class="site-author-image" itemprop="image"
src="/images/myPhoto.jpg"
alt="赖彬鸿" />
<p class="site-author-name" itemprop="name">赖彬鸿</p>
<p class="site-description motion-element" itemprop="description"></p>
</div>
<nav class="site-state motion-element">
<div class="site-state-item site-state-posts">
<a href="/archives/">
<span class="site-state-item-count">135</span>
<span class="site-state-item-name">日志</span>
</a>
</div>
<div class="site-state-item site-state-categories">
<a href="/categories/index.html">
<span class="site-state-item-count">32</span>
<span class="site-state-item-name">分类</span>
</a>
</div>
<div class="site-state-item site-state-tags">
<a href="/tags/index.html">
<span class="site-state-item-count">40</span>
<span class="site-state-item-name">标签</span>
</a>
</div>
</nav>
<div class="feed-link motion-element">
<a href="/atom.xml" rel="alternate">
<i class="fa fa-rss"></i>
RSS
</a>
</div>
<div class="links-of-author motion-element">
<span class="links-of-author-item">
<a href="https://github.com/LbhFront-end" target="_blank" title="GitHub">
<i class="fa fa-fw fa-github"></i>GitHub</a>
</span>
<span class="links-of-author-item">
<a href="https://www.cnblogs.com/lbh2018/" target="_blank" title="博客园">
<i class="fa fa-fw fa-globe"></i>博客园</a>
</span>
<span class="links-of-author-item">
<a href="https://yq.aliyun.com/users/1802204154913774?spm=a2c4e.11153940.blogcont662526.4.6c0a34f6E2lR5o" target="_blank" title="云栖">
<i class="fa fa-fw fa-globe"></i>云栖</a>
</span>
<span class="links-of-author-item">
<a href="mailto:544289495@qq.com" target="_blank" title="E-Mail">
<i class="fa fa-fw fa-envelope"></i>E-Mail</a>
</span>
<span class="links-of-author-item">
<a href="tencent://AddContact/?fromId=45&fromSubId=1&subcmd=all&uin=544289495&website=www.oicqzone.com" target="_blank" title="QQ">
<i class="fa fa-fw fa-qq"></i>QQ</a>
</span>
<span class="links-of-author-item">
<a href="https://www.google.com.hk/search?safe=strict&source=hp&ei=JtLCXIriJ8G4-gS_-4qABQ&q=site%3Alaibh.top&btnK=Google+%E6%90%9C%E7%B4%A2&oq=site%3Alaibh.top&gs_l=psy-ab.3...1158.6834..7051...5.0..1.246.3720.2-17......0....1..gws-wiz.....0..0j0i10.rJMUHvdrbds" target="_blank" title="Google">
<i class="fa fa-fw fa-google"></i>Google</a>
</span>
</div>
<iframe frameborder="no" border="0" marginwidth="0" marginheight="0" width=330 height=90 src="//music.163.com/outchain/player?type=0&id=2353471182&auto=0&height=90"></iframe>
<div class="links-of-blogroll motion-element links-of-blogroll-inline">
<div class="links-of-blogroll-title">
<i class="fa fa-fw fa-link"></i>
友情链接
</div>
<ul class="links-of-blogroll-list">
<li class="links-of-blogroll-item">
<a href="http://www.chjtx.com/JRoll/" title="醉萝卜" target="_blank">醉萝卜</a>
</li>
<li class="links-of-blogroll-item">
<a href="http://hzd.plus/" title="Zhendong" target="_blank">Zhendong</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://www.cnblogs.com/cnyball" title="cnyballk" target="_blank">cnyballk</a>
</li>
<li class="links-of-blogroll-item">
<a href="http://johnzz.top/" title="John" target="_blank">John</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://xiaojun1994.top/" title="xiaojun1994" target="_blank">xiaojun1994</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://me.ursb.me" title="Airing" target="_blank">Airing</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://www.iyouhun.com" title="游魂" target="_blank">游魂</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://icoty.github.io/" title="荒野之萍" target="_blank">荒野之萍</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://im-one.github.io/" title="imOne" target="_blank">imOne</a>
</li>
<li class="links-of-blogroll-item">
<a href="http://blog.hourxu.com/" title="Ambre" target="_blank">Ambre</a>
</li>
<li class="links-of-blogroll-item">
<a href="http://www.huyujs.com" title="胡雨" target="_blank">胡雨</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://www.andou.live" title="安逗" target="_blank">安逗</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://www.jianshu.com/u/701a8bbf4f7e" title="陈健斌" target="_blank">陈健斌</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://itobys.github.io/" title="汤姆Tom酱" target="_blank">汤姆Tom酱</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://breeze2.github.io/blog/" title="林毅锋" target="_blank">林毅锋</a>
</li>
<li class="links-of-blogroll-item">
<a href="http://www.qzroc.com/" title="大鹏博客" target="_blank">大鹏博客</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://lyreal666.com/" title="余腾靖的博客" target="_blank">余腾靖的博客</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://buzuosheng.com/" title="不作声" target="_blank">不作声</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://www.baidu.com/s?ie=UTF-8&wd=site%3Alaibh.top" title="百度" target="_blank">百度</a>
</li>
<li class="links-of-blogroll-item">
<a href="https://www.google.com.hk/search?safe=strict&source=hp&ei=zXdWXfemLJbO0PEP8qyXyA0&q=site%3Alaibh.top&oq=site%3Alaibh.top&gs_l=psy-ab.3...580.8501..8767...0.0..0.397.934.2-1j2......0....2j1..gws-wiz.QESXfWGadT0&ved=0ahUKEwi3wbusiofkAhUWJzQIHXLWBdkQ4dUDCAU&uact=5" title="谷歌" target="_blank">谷歌</a>
</li>
</ul>
</div>
</div>
</section>
<!--noindex-->
<section class="post-toc-wrap motion-element sidebar-panel sidebar-panel-active">
<div class="post-toc">
<div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-3"><a class="nav-link" href="#原文地址：深入浅出JavaScript运行机制"><span class="nav-number">1.</span> <span class="nav-text">原文地址：深入浅出JavaScript运行机制</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#（转）深入浅出JavaScript-运行机制"><span class="nav-number"></span> <span class="nav-text">（转）深入浅出JavaScript 运行机制</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#一、引子"><span class="nav-number">1.</span> <span class="nav-text">一、引子</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#二、理解JS的单线程的概念"><span class="nav-number">2.</span> <span class="nav-text">二、理解JS的单线程的概念</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#三、理解任务队列-消息队列"><span class="nav-number">3.</span> <span class="nav-text">三、理解任务队列(消息队列)</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#四、理解Event-Loop"><span class="nav-number">4.</span> <span class="nav-text">四、理解Event Loop</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#五、哪些语句会放入异步任务队列及放入时机"><span class="nav-number">5.</span> <span class="nav-text">五、哪些语句会放入异步任务队列及放入时机</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#七、题外话"><span class="nav-number">6.</span> <span class="nav-text">七、题外话</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#八、参考资料"><span class="nav-number">7.</span> <span class="nav-text">八、参考资料</span></a></li></ol></div>
</div>
</section>
<!--/noindex-->
</div>
</aside>
</div>
</main>
<footer id="footer" class="footer">
<div class="footer-inner">
<script async src="//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script>
<div class="copyright">© 2018 — <span itemprop="copyrightYear">2022</span>
<span class="with-love">
<i class="fa fa-heart throb" style="color: #d43f57;"></i>
</span>
<span class="author" itemprop="copyrightHolder">赖彬鸿</span>
</div>
<script src='https://unpkg.com/mermaid@7.1.2/dist/mermaid.min.js'></script>
<script>
if (window.mermaid) {
mermaid.initialize("");
}
</script>
<!--
<div class="powered-by">由 <a class="theme-link" target="_blank" href="https://hexo.io">Hexo</a> 强力驱动</div>
<span class="post-meta-divider">|</span>
<div class="theme-info">主题 — <a class="theme-link" target="_blank" href="https://github.com/iissnan/hexo-theme-next">NexT.Mist</a> v5.1.4</div>
-->
<div>
<span id="busuanzi_container_site_pv" title="访问量">
<i class="fa fa fa-eye"></i> <span id="busuanzi_value_site_pv"></span>
</span>
<span id="busuanzi_container_site_uv" title="访问人数">
<i class="fa fa-user"></i> <span id="busuanzi_value_site_uv"></span>
</span>
<span class="post-count" title="博客总字数"><i class="fa fa-pagelines" aria-hidden="true"></i>745.9k</span>
</div>
<i class="fa fa-shield" aria-hidden="true" title="本站安全运行时间"></i> <span id="timeDate">载入天数...</span><span id="times">载入时分秒...</span>
<script>
var now = new Date();
function createtime() {
var grt= new Date("01/29/2018 09:47:04");//此处修改你的建站时间或者网站上线时间
now.setTime(now.getTime()+250);
days = (now - grt ) / 1000 / 60 / 60 / 24; dnum = Math.floor(days);
hours = (now - grt ) / 1000 / 60 / 60 - (24 * dnum); hnum = Math.floor(hours);
if(String(hnum).length ==1 ){hnum = "0" + hnum;} minutes = (now - grt ) / 1000 /60 - (24 * 60 * dnum) - (60 * hnum);
mnum = Math.floor(minutes); if(String(mnum).length ==1 ){mnum = "0" + mnum;}
seconds = (now - grt ) / 1000 - (24 * 60 * 60 * dnum) - (60 * 60 * hnum) - (60 * mnum);
snum = Math.round(seconds);
if(String(snum).length ==1 ){snum = "0" + snum;}
document.getElementById("timeDate").innerHTML = dnum+" 天 ";
document.getElementById("times").innerHTML = hnum + " 小时 " + mnum + " 分 " + snum + " 秒";
}
setInterval("createtime()",250);
</script>
</div>
</footer>
<div class="back-to-top">
<i class="fa fa-arrow-up"></i>
<span id="scrollpercent"><span>0</span>%</span>
</div>