-
Notifications
You must be signed in to change notification settings - Fork 13
Expand file tree
/
Copy pathmap.html
More file actions
115 lines (97 loc) · 41.2 KB
/
map.html
File metadata and controls
115 lines (97 loc) · 41.2 KB
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
<!DOCTYPE html>
<html lang="en-US">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1">
<title>JavsScript - Map</title>
<meta name="generator" content="VuePress 1.8.2">
<link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png">
<link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png">
<link rel="manifest" href="/site.webmanifest">
<link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png">
<link rel="mask-icon" href="/safari-pinned-tab.svg" color="#5bbad5">
<meta name="description" content="Creating a Map, Clearing a Map, Removing an element from a Map, Checking if a key exists in a Map, Iterating Maps, Getting and setting elements, Getting the number of elements of a Map">
<meta property="og:site_name" content="DevTut">
<meta property="og:title" content="JavsScript - Map">
<meta property="og:description" content="Creating a Map, Clearing a Map, Removing an element from a Map, Checking if a key exists in a Map, Iterating Maps, Getting and setting elements, Getting the number of elements of a Map">
<meta property="og:type" content="article">
<meta property="og:url" content="/javascript/map.html">
<meta property="og:image" content="/logo.png">
<meta name="twitter:title" content="JavsScript - Map">
<meta name="twitter:description" content="Creating a Map, Clearing a Map, Removing an element from a Map, Checking if a key exists in a Map, Iterating Maps, Getting and setting elements, Getting the number of elements of a Map">
<meta name="twitter:url" content="/javascript/map.html">
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:image" content="/logo.png">
<meta name="theme-color" content="#ffffff">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<meta name="msapplication-TileImage" content="/mstile-150x150.png">
<meta name="msapplication-TileColor" content="#da532c">
<meta name="google-site-verification" content="76_rKXgwMVIjd-axJC_1zPV9OS4mEjvtgjYOWVkAdnQ">
<link rel="preload" href="/assets/css/0.styles.60619e34.css" as="style"><link rel="preload" href="/assets/js/app.1779e102.js" as="script"><link rel="preload" href="/assets/js/3.2cfa8016.js" as="script"><link rel="preload" href="/assets/js/1760.33f43b79.js" as="script">
<link rel="stylesheet" href="/assets/css/0.styles.60619e34.css">
</head>
<body>
<div id="app" data-server-rendered="true"><div class="theme-container"><header class="navbar"><div class="sidebar-button"><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" role="img" viewBox="0 0 448 512" class="icon"><path fill="currentColor" d="M436 124H12c-6.627 0-12-5.373-12-12V80c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12z"></path></svg></div> <a href="/" class="home-link router-link-active"><!----> <span class="site-name">DevTut</span></a> <div class="links"><form id="search-form" role="search" class="algolia-search-wrapper search-box"><input id="algolia-search-input" class="search-query"></form> <nav class="nav-links can-hide"> <a href="https://github.com/devtut/generate" target="_blank" rel="noopener noreferrer" class="repo-link">
GitHub
<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav></div></header> <div class="sidebar-mask"></div> <aside class="sidebar"><nav class="nav-links"> <a href="https://github.com/devtut/generate" target="_blank" rel="noopener noreferrer" class="repo-link">
GitHub
<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav> <ul class="sidebar-links"><li><section class="sidebar-group depth-0"><p class="sidebar-heading open"><span>JavaScript</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/javascript/" aria-current="page" class="sidebar-link">Disclaimer</a></li><li><a href="/javascript/getting-started-with-javascript.html" class="sidebar-link">Getting started with JavaScript</a></li><li><a href="/javascript/javascript-variables.html" class="sidebar-link">JavaScript Variables</a></li><li><a href="/javascript/built-in-constants.html" class="sidebar-link">Built-in Constants</a></li><li><a href="/javascript/comments.html" class="sidebar-link">Comments</a></li><li><a href="/javascript/console.html" class="sidebar-link">Console</a></li><li><a href="/javascript/datatypes-in-javascript.html" class="sidebar-link">Datatypes in Javascript</a></li><li><a href="/javascript/strings.html" class="sidebar-link">Strings</a></li><li><a href="/javascript/date.html" class="sidebar-link">Date</a></li><li><a href="/javascript/date-comparison.html" class="sidebar-link">Date Comparison</a></li><li><a href="/javascript/comparison-operations.html" class="sidebar-link">Comparison Operations</a></li><li><a href="/javascript/conditions.html" class="sidebar-link">Conditions</a></li><li><a href="/javascript/arrays.html" class="sidebar-link">Arrays</a></li><li><a href="/javascript/objects.html" class="sidebar-link">Objects</a></li><li><a href="/javascript/arithmetic-math.html" class="sidebar-link">Arithmetic (Math)</a></li><li><a href="/javascript/bitwise-operators.html" class="sidebar-link">Bitwise operators</a></li><li><a href="/javascript/constructor-functions.html" class="sidebar-link">Constructor functions</a></li><li><a href="/javascript/declarations-and-assignments.html" class="sidebar-link">Declarations and Assignments</a></li><li><a href="/javascript/loops.html" class="sidebar-link">Loops</a></li><li><a href="/javascript/functions.html" class="sidebar-link">Functions</a></li><li><a href="/javascript/functional-javascript.html" class="sidebar-link">Functional JavaScript</a></li><li><a href="/javascript/prototypes-objects.html" class="sidebar-link">Prototypes, objects</a></li><li><a href="/javascript/classes.html" class="sidebar-link">Classes</a></li><li><a href="/javascript/namespacing.html" class="sidebar-link">Namespacing</a></li><li><a href="/javascript/context-this.html" class="sidebar-link">Context (this)</a></li><li><a href="/javascript/setters-and-getters.html" class="sidebar-link">Setters and Getters</a></li><li><a href="/javascript/events.html" class="sidebar-link">Events</a></li><li><a href="/javascript/inheritance.html" class="sidebar-link">Inheritance</a></li><li><a href="/javascript/method-chaining.html" class="sidebar-link">Method Chaining</a></li><li><a href="/javascript/callbacks.html" class="sidebar-link">Callbacks</a></li><li><a href="/javascript/intervals-and-timeouts.html" class="sidebar-link">Intervals and Timeouts</a></li><li><a href="/javascript/regular-expressions.html" class="sidebar-link">Regular expressions</a></li><li><a href="/javascript/cookies.html" class="sidebar-link">Cookies</a></li><li><a href="/javascript/web-storage.html" class="sidebar-link">Web Storage</a></li><li><a href="/javascript/data-attributes.html" class="sidebar-link">Data attributes</a></li><li><a href="/javascript/json.html" class="sidebar-link">JSON</a></li><li><a href="/javascript/ajax.html" class="sidebar-link">AJAX</a></li><li><a href="/javascript/enumerations.html" class="sidebar-link">Enumerations</a></li><li><a href="/javascript/map.html" aria-current="page" class="active sidebar-link">Map</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/javascript/map.html#creating-a-map" class="sidebar-link">Creating a Map</a></li><li class="sidebar-sub-header"><a href="/javascript/map.html#clearing-a-map" class="sidebar-link">Clearing a Map</a></li><li class="sidebar-sub-header"><a href="/javascript/map.html#removing-an-element-from-a-map" class="sidebar-link">Removing an element from a Map</a></li><li class="sidebar-sub-header"><a href="/javascript/map.html#checking-if-a-key-exists-in-a-map" class="sidebar-link">Checking if a key exists in a Map</a></li><li class="sidebar-sub-header"><a href="/javascript/map.html#iterating-maps" class="sidebar-link">Iterating Maps</a></li><li class="sidebar-sub-header"><a href="/javascript/map.html#getting-and-setting-elements" class="sidebar-link">Getting and setting elements</a></li><li class="sidebar-sub-header"><a href="/javascript/map.html#getting-the-number-of-elements-of-a-map" class="sidebar-link">Getting the number of elements of a Map</a></li></ul></li><li><a href="/javascript/timestamps.html" class="sidebar-link">Timestamps</a></li><li><a href="/javascript/unary-operators.html" class="sidebar-link">Unary Operators</a></li><li><a href="/javascript/generators.html" class="sidebar-link">Generators</a></li><li><a href="/javascript/promises.html" class="sidebar-link">Promises</a></li><li><a href="/javascript/set.html" class="sidebar-link">Set</a></li><li><a href="/javascript/modals-prompts.html" class="sidebar-link">Modals - Prompts</a></li><li><a href="/javascript/execcommand-and-contenteditable.html" class="sidebar-link">execCommand and contenteditable</a></li><li><a href="/javascript/history.html" class="sidebar-link">History</a></li><li><a href="/javascript/navigator-object.html" class="sidebar-link">Navigator Object</a></li><li><a href="/javascript/bom-browser-object-model.html" class="sidebar-link">BOM (Browser Object Model)</a></li><li><a href="/javascript/the-event-loop.html" class="sidebar-link">The Event Loop</a></li><li><a href="/javascript/strict-mode.html" class="sidebar-link">Strict mode</a></li><li><a href="/javascript/custom-elements.html" class="sidebar-link">Custom Elements</a></li><li><a href="/javascript/data-manipulation.html" class="sidebar-link">Data Manipulation</a></li><li><a href="/javascript/binary-data.html" class="sidebar-link">Binary Data</a></li><li><a href="/javascript/template-literals.html" class="sidebar-link">Template Literals</a></li><li><a href="/javascript/fetch.html" class="sidebar-link">Fetch</a></li><li><a href="/javascript/scope.html" class="sidebar-link">Scope</a></li><li><a href="/javascript/modules.html" class="sidebar-link">Modules</a></li><li><a href="/javascript/screen.html" class="sidebar-link">Screen</a></li><li><a href="/javascript/variable-coercion-conversion.html" class="sidebar-link">Variable coercion/conversion</a></li><li><a href="/javascript/destructuring-assignment.html" class="sidebar-link">Destructuring assignment</a></li><li><a href="/javascript/websockets.html" class="sidebar-link">WebSockets</a></li><li><a href="/javascript/arrow-functions.html" class="sidebar-link">Arrow Functions</a></li><li><a href="/javascript/workers.html" class="sidebar-link">Workers</a></li><li><a href="/javascript/requestanimationframe.html" class="sidebar-link">requestAnimationFrame</a></li><li><a href="/javascript/creational-design-patterns.html" class="sidebar-link">Creational Design Patterns</a></li><li><a href="/javascript/detecting-browser.html" class="sidebar-link">Detecting browser</a></li><li><a href="/javascript/symbols.html" class="sidebar-link">Symbols</a></li><li><a href="/javascript/transpiling.html" class="sidebar-link">Transpiling</a></li><li><a href="/javascript/automatic-semicolon-insertion-asi.html" class="sidebar-link">Automatic Semicolon Insertion - ASI</a></li><li><a href="/javascript/localization.html" class="sidebar-link">Localization</a></li><li><a href="/javascript/geolocation.html" class="sidebar-link">Geolocation</a></li><li><a href="/javascript/indexeddb.html" class="sidebar-link">IndexedDB</a></li><li><a href="/javascript/modularization-techniques.html" class="sidebar-link">Modularization Techniques</a></li><li><a href="/javascript/proxy.html" class="sidebar-link">Proxy</a></li><li><a href="/javascript/postmessage-and-messageevent.html" class="sidebar-link">.postMessage() and MessageEvent</a></li><li><a href="/javascript/weakmap.html" class="sidebar-link">WeakMap</a></li><li><a href="/javascript/weakset.html" class="sidebar-link">WeakSet</a></li><li><a href="/javascript/escape-sequences.html" class="sidebar-link">Escape Sequences</a></li><li><a href="/javascript/behavioral-design-patterns.html" class="sidebar-link">Behavioral Design Patterns</a></li><li><a href="/javascript/server-sent-events.html" class="sidebar-link">Server-sent events</a></li><li><a href="/javascript/async-functions-async-await.html" class="sidebar-link">Async functions (async/await)</a></li><li><a href="/javascript/async-iterators.html" class="sidebar-link">Async Iterators</a></li><li><a href="/javascript/how-to-make-iterator-usable-inside-async-callback-function.html" class="sidebar-link">How to make iterator usable inside async callback function</a></li><li><a href="/javascript/tail-call-optimization.html" class="sidebar-link">Tail Call Optimization</a></li><li><a href="/javascript/bitwise-operators-real-world-examples-snippets.html" class="sidebar-link">Bitwise Operators - Real World Examples (snippets)</a></li><li><a href="/javascript/tilde.html" class="sidebar-link">Tilde ~</a></li><li><a href="/javascript/using-javascript-to-get-set-css-custom-variables.html" class="sidebar-link">Using javascript to get/set CSS custom variables</a></li><li><a href="/javascript/selection-api.html" class="sidebar-link">Selection API</a></li><li><a href="/javascript/file-api-blobs-and-filereaders.html" class="sidebar-link">File API, Blobs and FileReaders</a></li><li><a href="/javascript/notifications-api.html" class="sidebar-link">Notifications API</a></li><li><a href="/javascript/vibration-api.html" class="sidebar-link">Vibration API</a></li><li><a href="/javascript/battery-status-api.html" class="sidebar-link">Battery Status API</a></li><li><a href="/javascript/fluent-api.html" class="sidebar-link">Fluent API</a></li><li><a href="/javascript/web-cryptography-api.html" class="sidebar-link">Web Cryptography API</a></li><li><a href="/javascript/security-issues.html" class="sidebar-link">Security issues</a></li><li><a href="/javascript/same-origin-policy-cross-origin-communication.html" class="sidebar-link">Same Origin Policy & Cross-Origin Communication</a></li><li><a href="/javascript/error-handling.html" class="sidebar-link">Error Handling</a></li><li><a href="/javascript/global-error-handling-in-browsers.html" class="sidebar-link">Global error handling in browsers</a></li><li><a href="/javascript/debugging.html" class="sidebar-link">Debugging</a></li><li><a href="/javascript/unit-testing-javascript.html" class="sidebar-link">Unit Testing Javascript</a></li><li><a href="/javascript/evaluating-javascript.html" class="sidebar-link">Evaluating JavaScript</a></li><li><a href="/javascript/linters-ensuring-code-quality.html" class="sidebar-link">Linters - Ensuring code quality</a></li><li><a href="/javascript/anti-patterns.html" class="sidebar-link">Anti-patterns</a></li><li><a href="/javascript/performance-tips.html" class="sidebar-link">Performance Tips</a></li><li><a href="/javascript/memory-efficiency.html" class="sidebar-link">Memory efficiency</a></li><li><a href="/javascript/reserved-keywords.html" class="sidebar-link">Reserved Keywords</a></li><li><a href="/javascript/contributors.html" class="sidebar-link">The Contributors</a></li></ul></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="map"><a href="#map" class="header-anchor">#</a> Map</h1> <h2 id="creating-a-map"><a href="#creating-a-map" class="header-anchor">#</a> Creating a Map</h2> <p>A Map is a basic mapping of keys to values. Maps are different from objects in that their keys can be anything (primitive values as well as objects), not just strings and symbols. Iteration over Maps is also always done in the order the items were inserted into the Map, whereas the order is undefined when iterating over keys in an object.</p> <p>To create a Map, use the Map constructor:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>It has an optional parameter, which can be any iterable object (for example an array) which contains arrays of two elements – first is the key, the seconds is the value. For example:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>foo<span class="token operator">:</span> <span class="token string">"bar"</span><span class="token punctuation">}</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span>document<span class="token punctuation">.</span>body<span class="token punctuation">,</span> <span class="token string">"body"</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// ^key ^value ^key ^value</span>
</code></pre></div><h2 id="clearing-a-map"><a href="#clearing-a-map" class="header-anchor">#</a> Clearing a Map</h2> <p>To remove all elements from a Map, use the <code>.clear()</code> method:</p> <div class="language-js extra-class"><pre class="language-js"><code>map<span class="token punctuation">.</span><span class="token function">clear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>Example:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span>size<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 2</span>
map<span class="token punctuation">.</span><span class="token function">clear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span>size<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 0</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// undefined</span>
</code></pre></div><h2 id="removing-an-element-from-a-map"><a href="#removing-an-element-from-a-map" class="header-anchor">#</a> Removing an element from a Map</h2> <p>To remove an element from a map use the <code>.delete()</code> method.</p> <div class="language-js extra-class"><pre class="language-js"><code>map<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>Example:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 4</span>
map<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// undefined</span>
</code></pre></div><p>This method returns <code>true</code> if the element existed and has been removed, otherwise <code>false</code>:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span><span class="token number">7</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
</code></pre></div><h2 id="checking-if-a-key-exists-in-a-map"><a href="#checking-if-a-key-exists-in-a-map" class="header-anchor">#</a> Checking if a key exists in a Map</h2> <p>To check if a key exists in a Map, use the <code>.has()</code> method:</p> <div class="language-js extra-class"><pre class="language-js"><code>map<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>Example:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
</code></pre></div><h2 id="iterating-maps"><a href="#iterating-maps" class="header-anchor">#</a> Iterating Maps</h2> <p>Map has three methods which returns iterators: <code>.keys()</code>, <code>.values()</code> and <code>.entries()</code>. <code>.entries()</code> is the default Map iterator, and contains <code>[key, value]</code> pairs.</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> <span class="token punctuation">[</span>key<span class="token punctuation">,</span> value<span class="token punctuation">]</span> <span class="token keyword">of</span> map<span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">key: </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">, value: </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>value<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// logs:</span>
<span class="token comment">// key: 1, value: 2</span>
<span class="token comment">// key: 3, value: 4</span>
<span class="token punctuation">}</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> key <span class="token keyword">of</span> map<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// logs 1 and 3</span>
<span class="token punctuation">}</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> value <span class="token keyword">of</span> map<span class="token punctuation">.</span><span class="token function">values</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>value<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// logs 2 and 4</span>
<span class="token punctuation">}</span>
</code></pre></div><p>Map also has <code>.forEach()</code> method. The first parameter is a callback function, which will be called for each element in the map, and the second parameter is the value which will be used as <code>this</code> when executing the callback function.</p> <p>The callback function has three arguments: value, key, and the map object.</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
map<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">value<span class="token punctuation">,</span> key<span class="token punctuation">,</span> theMap</span><span class="token punctuation">)</span> <span class="token operator">=></span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">key: </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>key<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">, value: </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>value<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// logs:</span>
<span class="token comment">// key: 1, value: 2</span>
<span class="token comment">// key: 3, value: 4</span>
</code></pre></div><h2 id="getting-and-setting-elements"><a href="#getting-and-setting-elements" class="header-anchor">#</a> Getting and setting elements</h2> <p>Use <code>.get(key)</code> to get value by key and <code>.set(key, value)</code> to assign a value to a key.</p> <p>If the element with the specified key doesn't exist in the map, <code>.get()</code> returns <code>undefined</code>.</p> <p><code>.set()</code> method returns the map object, so you can chain <code>.set()</code> calls.</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// undefined</span>
map<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 2</span>
</code></pre></div><h2 id="getting-the-number-of-elements-of-a-map"><a href="#getting-the-number-of-elements-of-a-map" class="header-anchor">#</a> Getting the number of elements of a Map</h2> <p>To get the numbers of elements of a Map, use the <code>.size</code> property:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span>size<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 2</span>
</code></pre></div><h4 id="syntax"><a href="#syntax" class="header-anchor">#</a> Syntax</h4> <ul><li>new Map([iterable])</li> <li>map.set(key, value)</li> <li>map.get(key)</li> <li>map.size</li> <li>map.clear()</li> <li>map.delete(key)</li> <li>map.entries()</li> <li>map.keys()</li> <li>map.values()</li> <li>map.forEach(callback[, thisArg])</li></ul> <h4 id="parameters"><a href="#parameters" class="header-anchor">#</a> Parameters</h4> <table><thead><tr><th>Parameter</th> <th>Details</th></tr></thead> <tbody><tr><td><code>iterable</code></td> <td>Any iterable object (for example an array) containing <code>[key, value]</code> pairs.</td></tr> <tr><td><code>key</code></td> <td>The key of an element.</td></tr> <tr><td><code>value</code></td> <td>The value assigned to the key.</td></tr> <tr><td><code>callback</code></td> <td>Callback function called with three parameters: value, key, and the map.</td></tr> <tr><td><code>thisArg</code></td> <td>Value which will be used as <code>this</code> when executing <code>callback</code>.</td></tr></tbody></table> <h4 id="remarks"><a href="#remarks" class="header-anchor">#</a> Remarks</h4> <p>In Maps <code>NaN</code> is considered to be the same as <code>NaN</code>, even though <code>NaN !== NaN</code>. For example:</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">NaN</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">NaN</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
</code></pre></div></div> <footer class="page-edit"><div class="edit-link"><a href="https://github.com/devtut/generate/edit/master/docs/javascript/map.md" target="_blank" rel="noopener noreferrer">Edit this page on GitHub</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev">
←
<a href="/javascript/enumerations.html" class="prev">
Enumerations
</a></span> <span class="next"><a href="/javascript/timestamps.html">
Timestamps
</a>
→
</span></p></div> </main></div><div class="global-ui"><!----></div></div>
<script src="/assets/js/app.1779e102.js" defer></script><script src="/assets/js/3.2cfa8016.js" defer></script><script src="/assets/js/1760.33f43b79.js" defer></script>
</body>
</html>