-
Notifications
You must be signed in to change notification settings - Fork 0
/
index.html
1779 lines (932 loc) · 52.4 KB
/
index.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 muse use-motion" lang="en">
<head>
<!-- hexo-inject:begin --><!-- hexo-inject:end --><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">
<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="//fonts.googleapis.com/css?family=Open Sans:300,300italic,400,400italic,700,700italic&subset=latin,latin-ext" 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=5.1.2" rel="stylesheet" type="text/css" />
<meta name="keywords" content="Hexo, NexT" />
<link rel="shortcut icon" type="image/x-icon" href="/favicon.ico?v=5.1.2" />
<meta property="og:type" content="website">
<meta property="og:title" content="Yanbin's Blog">
<meta property="og:url" content="my-jabin.github.io/index.html">
<meta property="og:site_name" content="Yanbin's Blog">
<meta property="og:locale" content="en">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="Yanbin's Blog">
<script type="text/javascript" id="hexo.configurations">
var NexT = window.NexT || {};
var CONFIG = {
root: '/',
scheme: 'Muse',
sidebar: {"position":"left","display":"hide","offset":12,"offset_float":12,"b2t":false,"scrollpercent":false,"onmobile":false},
fancybox: true,
tabs: true,
motion: true,
duoshuo: {
userId: '0',
author: 'Author'
},
algolia: {
applicationID: '',
apiKey: '',
indexName: '',
hits: {"per_page":10},
labels: {"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}
}
};
</script>
<link rel="canonical" href="my-jabin.github.io/"/>
<title>Yanbin's Blog</title>
<script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-109176342-1', 'auto');
ga('send', 'pageview');
</script><!-- hexo-inject:begin --><!-- hexo-inject:end -->
</head>
<body itemscope itemtype="http://schema.org/WebPage" lang="en">
<!-- hexo-inject:begin --><!-- hexo-inject:end --><div class="container sidebar-position-left
page-home
">
<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">Yanbin's Blog</span>
<span class="logo-line-after"><i></i></span>
</a>
</div>
<p class="site-subtitle">Stay hungry. Stay foolish.</p>
</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 />
Home
</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 />
Categories
</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 />
Tags
</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 />
Archives
</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 />
Search
</a>
</li>
</ul>
<div class="site-search">
<div class="popup search-popup local-search-popup">
<div class="local-search-header clearfix">
<span class="search-icon">
<i class="fa fa-search"></i>
</span>
<span class="popup-btn-close">
<i class="fa fa-times-circle"></i>
</span>
<div class="local-search-input-wrapper">
<input autocomplete="off"
placeholder="Searching..." spellcheck="false"
type="text" id="local-search-input">
</div>
</div>
<div id="local-search-result"></div>
</div>
</div>
</nav>
</div>
</header>
<main id="main" class="main">
<div class="main-inner">
<div class="content-wrap">
<div id="content" class="content">
<section 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="my-jabin.github.io/Algorithm/2018-04-18-ISAM-and-B-trees/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="name" content="Yanbin Hu">
<meta itemprop="description" content="">
<meta itemprop="image" content="/images/avatar.jpg">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yanbin's Blog">
</span>
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/Algorithm/2018-04-18-ISAM-and-B-trees/" itemprop="url">ISAM and B+ trees</a></h1>
<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">Posted on</span>
<time title="Post created" itemprop="dateCreated datePublished" datetime="2018-04-18T16:42:52+02:00">
2018-04-18
</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">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Algorithm/" itemprop="url" rel="index">
<span itemprop="name">Algorithm</span>
</a>
</span>
</span>
<span class="post-comments-count">
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-comment-o"></i>
</span>
<a href="/Algorithm/2018-04-18-ISAM-and-B-trees/#comments" itemprop="discussionUrl">
<span class="post-comments-count disqus-comment-count"
data-disqus-identifier="/Algorithm/2018-04-18-ISAM-and-B-trees/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<p>How could we search the query in a certain range?<br><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> *</span><br><span class="line"><span class="keyword">FROM</span> CUSTOMERS</span><br><span class="line"><span class="keyword">WHERE</span> ZIPCODE <span class="keyword">BETWEEN</span> <span class="number">8880</span> <span class="keyword">AND</span> <span class="number">8999</span></span><br></pre></td></tr></table></figure></p>
<p>We could</p>
<ol>
<li>sort the table on disk(in ZIPCODE order)</li>
<li>use binary search to find the <code>8880</code>, then sequential scan until ZIPCODE < 8999</li>
</ol>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/1.png">
<p>We need to read log(#tuple) tuples during the binary search phase. Once we find the lower range limit, we start sequential scan until the upper limit. If the range is huge, the initial binary search can be quite expensive, since the cost is proportional to the number of pages fetched.</p>
<p>In this article we introduce two index data structures, called ISAM and B+ tree. These structures provide efficient support for range selection, insertion and deletion. They also support for equality selections, although they are not as efficient as hash-based indexes.</p>
<h2 id="Indexed-Sequential-Access-Method-ISAM"><a href="#Indexed-Sequential-Access-Method-ISAM" class="headerlink" title="Indexed Sequential Access Method(ISAM)"></a>Indexed Sequential Access Method(ISAM)</h2><p>We use the <code>index file</code>, its structures is as following. Pairs of the form <key, pointer=""> is referred as <code>entry</code>. <code>Key</code> is the minimal value on the page that pointer points to.</key,></p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/2.png">
<p>Note that each index file contains more entries and each key serves as a <em>sperator</em> for the content of the pages pointed to by the pointer to its left and right.</p>
<p><strong>One-level ISAM structure</strong></p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/3.png">
<p>To support range selection, we search on the index file for a key of lower limit. Then we start a sequential scan of the data file from the page pointed to by the entry pointer.</p>
<p>It’s faster searching on the index file then on the data file, because the size of the index file is much more smaller then the data file size.</p>
<p><strong>Multi-level ISAM structure</strong></p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/4.png">
<p>If we want to insert some records into database, overflow pages might be created in order to insert data into. The ISAM tree remains <strong>static</strong>, so insertions and deletions in the data file do not affect the tree layers.</p>
<p>If a new record is going to be inserted and there is no space left on the associated page, we need to create a overflow page and hang it to the leaf page.</p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/5.png">
<p>Note that records on the overflow pages are not ordered in general.</p>
<p>Example:<br>We insert the records with key 23,48,41,42.</p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/6.png">
<p>Problems of ISAM:</p>
<ul>
<li>Maintenance of the overflow pages is required and records in the overflow pages is not ordered. Cost is expensive.</li>
<li>ISAM tree lose the balance after updating. It might lead to low performance.</li>
<li>ISAM tree is static, the non-leaf levels remains the same.</li>
</ul>
<h2 id="B-tree"><a href="#B-tree" class="headerlink" title="B+ tree"></a>B+ tree</h2><p>The B+ tree is derived from the ISAM tree, but is fully dynamic with respect to updates:</p>
<ul>
<li>Search performance is only dependent on the height of the B+ tree.</li>
<li>No overflow pages, B+ tree remains balance.</li>
<li>B+ tree offers efficient insert/delete procedures, the underlying data file can grow/shrink dynamically</li>
<li>B+ tree nodes(desipte the root page) are guaranteed to have a minimun occupany of 50%.</li>
</ul>
<p>B+ tree is similar to ISAM tree, but</p>
<ul>
<li>the leaf nodes are connected via a <strong>double-linked list</strong></li>
<li>leaves may contain actual data records or just <strong>reference</strong> to records.(reference is the common case)</li>
</ul>
<p>Each node of the B+ tree contains <em>n</em> entries, where $d \leq n \leq 2d$. The value <em>d</em> is a parameter of the B+ tree, called the <em>order</em> of the tree and is a measure of the capacity of a tree node. The root node is the only exception to this requirement on the number of entries: for the root, it is simply required that $1 \leq n \leq 2d$</p>
<p>Note that each node contains <em>n+1</em> pointers. Pointer $p_i$( $1 \leq i \leq i$) points to a subtree in which all key value <em>k</em> are $k_i \leq k < k_i+1$</p>
<p>Example:<br><img src="/Algorithm/2018-04-18-ISAM-and-B-trees/7.png"></p>
<h3 id="Insert"><a href="#Insert" class="headerlink" title="Insert"></a>Insert</h3><p>If we want to insert a record, we should:</p>
<ul>
<li>find the leaf page where it belongs.</li>
<li>if the page has enough space, simply insert it.</li>
<li>otherwise node p must be split into p and p’ and a new separator has to be inserted into the parent of p. Splitting happens recursively and may eventually lead to a split of root node.</li>
<li>distribute then entries of p and the new entry <k,p> onto pages p and p’</k,p></li>
</ul>
<p>We use the above example to demonstrate the insertion process. Suppose we want to insert record with key = 8 into the B+ tree.</p>
<ul>
<li>The minimal key value in the root page is 13, then 8 should be inserted into the page that the left pointer of 13 points to. It’s the node with value {2,3,5,7}</li>
<li>The page has no more space, it has to be split into two pages. Entries {2,3} remains on page p, entries {5,7,8} go to new page p’.</li>
<li>Since we spilt a page, a new separator is also created, the value of the separator is the value of the first entry of the new page p’, here is 5.</li>
<li>Insert separator into parent node. Since parent node is also full, it has to be split too. If the parent is not a root node, it splits like a normal node. If it’s a root node, it splits a little bit different.</li>
</ul>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/8.png">
<p><strong>Root node split</strong>:<br>Now the root node should be split, if the new separator is inserted, it has {5,13,17,24,30}. We simply create a new root node which hold only the middle entry. Here entry 17 is pushed up.</p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/9.png">
<p>Note that, splitting the old root and creating a new root node is the <em>only</em> situation in which the B+ tree height increase. The B+ tree remains balanced.</p>
<h3 id="Delete"><a href="#Delete" class="headerlink" title="Delete"></a>Delete</h3><p>Deletion is the opposite to the insertion.</p>
<p>Here we denote $m$ the number of entries of page p and $d$ is the order of B+ tree.<br>To delete a record with key <em>k</em></p>
<ul>
<li>find the page where <em>k</em> belongs to.</li>
<li>if $m>d$, then page p has enough occupancy, simply delete <em>k</em> from page p.</li>
<li>otherwise borrow a entry from its right(left) sibling</li>
<li>If its right(left) sibling has less then $d$ entries, merging leaf nodes is required.</li>
</ul>
<p>Example:</p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/10.png">
<p>If we continue to delete entry 20</p>
<ul>
<li>page p is underflow(m=1 < 2=d). We now borrow an entry 24 from its right sibling p’(p’ is not underflow since it has 3 entries)</li>
<li>The smallest key value(27) on page p’ is the new separator of p and p’ in their common parent.</li>
</ul>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/11.png">
<p>Now we continue to delete 24 from page p. We cannot borrow an entry from its sibling since its sibling is underflow. We should merge those two pages p and p’.</p>
<ul>
<li>Move all entries from p’ to p, then delete page p’.</li>
<li>Separator 27 between p and p’ is no longer needed and thus deleted from the parent.</li>
</ul>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/12.png">
<p>However the parent page has only one entry 30 and is thus underflow, it should borrow one entry from its left sibling, but its sibling has only <em>d=2</em> entries, thus those two pages has to be merged. It leads to the merge of root node.</p>
<p><strong>Root merge</strong></p>
<p>We simply pull the entry in the root page down to form a new merged node. The old root node is deleted and the new merged node becomes the root node.</p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/13.png">
<p>Finally the B+ tree looks like:</p>
<img src="/Algorithm/2018-04-18-ISAM-and-B-trees/14.png">
<p>Note that this is the only situation in which the B+ tree height decreases. The B+ tree remains balanced.</p>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</div>
</article>
<article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
<div class="post-block">
<link itemprop="mainEntityOfPage" href="my-jabin.github.io/RxJava/2018-04-14-RxJava2-Tutorial-Basic/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="name" content="Yanbin Hu">
<meta itemprop="description" content="">
<meta itemprop="image" content="/images/avatar.jpg">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yanbin's Blog">
</span>
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/RxJava/2018-04-14-RxJava2-Tutorial-Basic/" itemprop="url">RxJava2 Tutorial Basic</a></h1>
<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">Posted on</span>
<time title="Post created" itemprop="dateCreated datePublished" datetime="2018-04-14T19:59:04+02:00">
2018-04-14
</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">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/RxJava/" itemprop="url" rel="index">
<span itemprop="name">RxJava</span>
</a>
</span>
</span>
<span class="post-comments-count">
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-comment-o"></i>
</span>
<a href="/RxJava/2018-04-14-RxJava2-Tutorial-Basic/#comments" itemprop="discussionUrl">
<span class="post-comments-count disqus-comment-count"
data-disqus-identifier="/RxJava/2018-04-14-RxJava2-Tutorial-Basic/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h2 id="1-What-are-RxJava-and-reactive-programming-In-reactive-programming-the-consumer-reacts-to-the-data-as-it-comes-in"><a href="#1-What-are-RxJava-and-reactive-programming-In-reactive-programming-the-consumer-reacts-to-the-data-as-it-comes-in" class="headerlink" title="1. What are RxJava and reactive programming In reactive programming, the consumer reacts to the data as it comes in."></a>1. What are RxJava and reactive programming In reactive programming, the consumer reacts to the data as it comes in.</h2><p>This is the reason why asynchronous programming is also called reactive programming. Reactive programming allows to propagates event changes to registered observers. >The Observer pattern has done right. ReactiveX is a combination of the best ideas from the Observer pattern, the Iterator pattern, and functional programming. RxJava is a library that lets you create applications in the reactive programming style. At its core, reactive programming provides a clean, efficient way of processing and reacting to streams of real-time data, including data with dynamic values. These data streams don’t necessarily have to take the form of traditional data types, as RxJava pretty much treats everything as a stream of data—everything from variables to properties, caches, and even user input events like clicks and swipes. The data emitted by each stream can either be a value, an error, or a “completed” signal, although you don’t necessarily have to implement the last two.<br></p>
<!--noindex-->
<div class="post-button text-center">
<a class="btn" href="/RxJava/2018-04-14-RxJava2-Tutorial-Basic/#more" rel="contents">
Read more »
</a>
</div>
<!--/noindex-->
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</div>
</article>
<article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
<div class="post-block">
<link itemprop="mainEntityOfPage" href="my-jabin.github.io/JavaScript/2017-11-03-Object-to-primitive-conversion/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="name" content="Yanbin Hu">
<meta itemprop="description" content="">
<meta itemprop="image" content="/images/avatar.jpg">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yanbin's Blog">
</span>
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/JavaScript/2017-11-03-Object-to-primitive-conversion/" itemprop="url">Object to primitive conversion</a></h1>
<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">Posted on</span>
<time title="Post created" itemprop="dateCreated datePublished" datetime="2017-11-03T10:29:07+01:00">
2017-11-03
</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">In</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 class="post-comments-count">
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-comment-o"></i>
</span>
<a href="/JavaScript/2017-11-03-Object-to-primitive-conversion/#comments" itemprop="discussionUrl">
<span class="post-comments-count disqus-comment-count"
data-disqus-identifier="/JavaScript/2017-11-03-Object-to-primitive-conversion/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<p>What happends when object are added <code>obj1 + obj2</code>, subtracted <code>obj1 - obj2</code> or printed using <code>alert(obj)</code>?<br>There are special methods in objects that do the conversion.<br>For object, there is no to-boolean conversion, because all objects are <code>true</code> in a boolean context. So there are only string and numeric conversion.<br>When we output an object like <code>alert(obj)</code>, it converts the object to string. String conversion happens usually in this situation.<br>The numeric conversion happens when we apply mathematical function. For instance, <code>Date</code> object can be suntracted, and the result <code>date1 - date2</code> is the time difference between two dates.<br></p>
<!--noindex-->
<div class="post-button text-center">
<a class="btn" href="/JavaScript/2017-11-03-Object-to-primitive-conversion/#more" rel="contents">
Read more »
</a>
</div>
<!--/noindex-->
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</div>
</article>
<article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
<div class="post-block">
<link itemprop="mainEntityOfPage" href="my-jabin.github.io/JavaScript/2017-11-02-Cloning-and-Merging-in-JavaScript/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="name" content="Yanbin Hu">
<meta itemprop="description" content="">
<meta itemprop="image" content="/images/avatar.jpg">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yanbin's Blog">
</span>
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/JavaScript/2017-11-02-Cloning-and-Merging-in-JavaScript/" itemprop="url">Cloning and Merging in JavaScript</a></h1>
<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">Posted on</span>
<time title="Post created" itemprop="dateCreated datePublished" datetime="2017-11-02T12:33:01+01:00">
2017-11-02
</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">In</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 class="post-comments-count">
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
<i class="fa fa-comment-o"></i>
</span>
<a href="/JavaScript/2017-11-02-Cloning-and-Merging-in-JavaScript/#comments" itemprop="discussionUrl">
<span class="post-comments-count disqus-comment-count"
data-disqus-identifier="/JavaScript/2017-11-02-Cloning-and-Merging-in-JavaScript/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h1 id="Cloning-and-merging-Object-assign"><a href="#Cloning-and-merging-Object-assign" class="headerlink" title="Cloning and merging, Object.assign"></a>Cloning and merging, Object.assign</h1><p>Copying an object variable creates one more reference to the same object. What if we need to duplicate an object?</p>
<p>We can use the method <code>Object.assign</code> for that:<br><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Object</span>.assign(dest[,src1,src2,...])</span><br></pre></td></tr></table></figure></p>
<p>It copies the properties of all object <code>src1, src2, ...</code> into <code>dest</code>. In other words, properties of all arguments starting from the 2nd are copied into the 1st, then it returns <code>dest</code><br></p>
<!--noindex-->
<div class="post-button text-center">
<a class="btn" href="/JavaScript/2017-11-02-Cloning-and-Merging-in-JavaScript/#more" rel="contents">
Read more »
</a>
</div>
<!--/noindex-->
</div>
<footer class="post-footer">