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authorPeter Bengtsson <mail@peterbe.com>2020-12-08 14:40:17 -0500
committerPeter Bengtsson <mail@peterbe.com>2020-12-08 14:40:17 -0500
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+---
+title: Set
+slug: Web/JavaScript/Reference/Global_Objects/Set
+tags:
+ - Class
+ - ECMAScript6
+ - JavaScript
+ - set
+ - 全局对象
+translation_of: Web/JavaScript/Reference/Global_Objects/Set
+---
+<div>{{ JSRef }}</div>
+
+<p><strong><code>Set</code></strong> 对象允许你存储任何类型的唯一值,无论是{{ Glossary('Primitive', '原始值') }}或者是对象引用。</p>
+
+<h2 id="简述">简述</h2>
+
+<p><code>Set</code>对象是值的集合,你可以按照插入的顺序迭代它的元素。 Set中的元素只会<strong>出现一次</strong>,即 Set 中的元素是唯一的。</p>
+
+<h3 id="值的相等">值的相等</h3>
+
+<p>因为 Set 中的值总是唯一的,所以需要判断两个值是否相等。在ECMAScript规范的早期版本中,这不是基于和===操作符中使用的算法相同的算法。具体来说,对于 Set s, +0 (+0 严格相等于-0)和-0是不同的值。然而,在 ECMAScript 2015规范中这点已被更改。有关详细信息,请参阅<a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Set#浏览器兼容性">浏览器兼容性</a> 表中的“<em>Key equality for -0 and 0</em>”。</p>
+
+<p>另外,<code>NaN</code>和<code>undefined</code>都可以被存储在Set 中, <code>NaN</code>之间被视为相同的值(NaN被认为是相同的,尽管 NaN !== NaN)。</p>
+
+<h2 id="Constructor">Constructor</h2>
+
+<dl>
+ <dt><a href="https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/Set"><code>Set()</code></a></dt>
+ <dd>创建一个新的<code>Set</code>对象。</dd>
+</dl>
+
+<h2 id="静态属性">静态属性</h2>
+
+<dl>
+ <dt>{{jsxref("Set.@@species", "get Set[@@species]")}}</dt>
+ <dd>构造函数用来创建派生对象.</dd>
+</dl>
+
+<h2 id="Properties" name="Properties">实例属性</h2>
+
+<dl>
+ <dt>{{jsxref("Set.prototype.size")}}</dt>
+ <dd>返回 Set 对象中的值的个数</dd>
+</dl>
+
+<h2 id="实例方法">实例方法</h2>
+
+<dl>
+ <dt>{{jsxref("Set.add", "Set.prototype.add(<em>value</em>)")}}</dt>
+ <dd>在<code>Set</code>对象尾部添加一个元素。返回该<code>Set</code>对象。</dd>
+ <dt>{{jsxref("Set.prototype.clear()")}}</dt>
+ <dd>移除<code>Set</code>对象内的所有元素。</dd>
+ <dt>{{jsxref("Set.delete", "Set.prototype.delete(<em>value</em>)")}}</dt>
+ <dd>移除<code>Set</code>中与这个值相等的元素,返回<code>Set.prototype.has(value)</code>在这个操作前会返回的值(即如果该元素存在,返回<code>true</code>,否则返回<code>false</code>)。<code>Set.prototype.has(value)</code>在此后会返回<code>false</code>。</dd>
+ <dt>{{jsxref("Set.prototype.entries()")}}</dt>
+ <dd>返回一个新的迭代器对象,该对象包含<code>Set</code>对象中的按插入顺序排列的所有元素的值的<code>[value, value]</code>数组。为了使这个方法和<code>Map</code>对象保持相似, 每个值的键和值相等。</dd>
+ <dt>{{jsxref("Set.forEach", "Set.prototype.forEach(<em>callbackFn</em>[, <em>thisArg</em>])")}}</dt>
+ <dd>按照插入顺序,为Set对象中的每一个值调用一次callBackFn。如果提供了<code>thisArg</code>参数,回调中的<code>this</code>会是这个参数。</dd>
+ <dt>{{jsxref("Set.has", "Set.prototype.has(<em>value</em>)")}}</dt>
+ <dd>返回一个布尔值,表示该值在<code>Set</code>中存在与否。</dd>
+ <dt>{{jsxref("Set.prototype.keys()")}}</dt>
+ <dd>与<strong><code>values()</code></strong>方法相同,返回一个新的迭代器对象,该对象包含<code>Set</code>对象中的按插入顺序排列的所有元素的值。</dd>
+ <dt>{{jsxref("Set.prototype.values()")}}</dt>
+ <dd>返回一个新的迭代器对象,该对象包含<code>Set</code>对象中的按插入顺序排列的所有元素的值。</dd>
+ <dt>{{jsxref("Set.prototype.@@iterator()", "Set.prototype[@@iterator]()")}}</dt>
+ <dd>返回一个新的迭代器对象,该对象包含<code>Set</code>对象中的按插入顺序排列的所有元素的值。</dd>
+</dl>
+
+<h2 id="示例">示例</h2>
+
+<h3 id="使用Set对象">使用<code>Set</code>对象</h3>
+
+<pre class="brush: js notranslate">let mySet = new Set();
+
+mySet.add(1); // Set [ 1 ]
+mySet.add(5); // Set [ 1, 5 ]
+mySet.add(5); // Set [ 1, 5 ]
+mySet.add("some text"); // Set [ 1, 5, "some text" ]
+let o = {a: 1, b: 2};
+mySet.add(o);
+
+mySet.add({a: 1, b: 2}); // o 指向的是不同的对象,所以没问题
+
+mySet.has(1); // true
+mySet.has(3); // false
+mySet.has(5); // true
+mySet.has(Math.sqrt(25)); // true
+mySet.has("Some Text".toLowerCase()); // true
+mySet.has(o); // true
+
+mySet.size; // 5
+
+mySet.delete(5); // true, 从set中移除5
+mySet.has(5); // false, 5已经被移除
+
+mySet.size; // 4, 刚刚移除一个值
+
+console.log(mySet);
+// logs Set(4) [ 1, "some text", {…}, {…} ] in Firefox
+// logs Set(4) { 1, "some text", {…}, {…} } in Chrome</pre>
+
+<h3 id="迭代Set">迭代Set</h3>
+
+<pre class="brush: js notranslate">// 迭代整个set
+// 按顺序输出:1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
+for (let item of mySet) console.log(item);
+
+// 按顺序输出:1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
+for (let item of mySet.keys()) console.log(item);
+
+// 按顺序输出:1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
+for (let item of mySet.values()) console.log(item);
+
+// 按顺序输出:1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
+//(键与值相等)
+for (let [key, value] of mySet.entries()) console.log(key);
+
+// 使用 Array.from 转换Set为Array
+var myArr = Array.from(mySet); // [1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}]
+
+// 如果在HTML文档中工作,也可以:
+mySet.add(document.body);
+mySet.has(document.querySelector("body")); // true
+
+// Set 和 Array互换
+mySet2 = new Set([1, 2, 3, 4]);
+mySet2.size; // 4
+[...mySet2]; // [1,2,3,4]
+
+// 可以通过如下代码模拟求交集
+let intersection = new Set([...set1].filter(x =&gt; set2.has(x)));
+
+// 可以通过如下代码模拟求差集
+let difference = new Set([...set1].filter(x =&gt; !set2.has(x)));
+
+// 用forEach迭代
+mySet.forEach(function(value) {
+ console.log(value);
+});
+
+// 1
+// 2
+// 3
+// 4
+</pre>
+
+<h3 id="实现基本集合操作">实现基本集合操作</h3>
+
+<pre class="brush: js notranslate">function isSuperset(set, subset) {
+ for (let elem of subset) {
+ if (!set.has(elem)) {
+ return false;
+ }
+ }
+ return true;
+}
+
+function union(setA, setB) {
+ let _union = new Set(setA);
+ for (let elem of setB) {
+ _union.add(elem);
+ }
+ return _union;
+}
+
+function intersection(setA, setB) {
+ let _intersection = new Set();
+ for (let elem of setB) {
+ if (setA.has(elem)) {
+ _intersection.add(elem);
+ }
+ }
+ return _intersection;
+}
+
+<code>function symmetricDifference(setA, setB) {
+ let _difference = new Set(setA);
+ for (let elem of setB) {
+ if (_difference.has(elem)) {
+ _difference.delete(elem);
+ } else {
+ _difference.add(elem);
+ }
+ }
+ return _difference;
+}</code>
+
+function difference(setA, setB) {
+ let _difference = new Set(setA);
+ for (let elem of setB) {
+ _difference.delete(elem);
+ }
+ return _difference;
+}
+
+//Examples
+let setA = new Set([1, 2, 3, 4]),
+ setB = new Set([2, 3]),
+ setC = new Set([3, 4, 5, 6]);
+
+isSuperset(setA, setB); // =&gt; true
+union(setA, setC); // =&gt; Set [1, 2, 3, 4, 5, 6]
+intersection(setA, setC); // =&gt; Set [3, 4]
+symmetricDifference(setA, setC); // =&gt; Set [1, 2, 5, 6]
+difference(setA, setC); // =&gt; Set [1, 2]
+</pre>
+
+<h3 id="Array_相关"> <code>Array</code> 相关</h3>
+
+<pre class="brush: js notranslate">let myArray = ["value1", "value2", "value3"];
+
+// 用Set构造器将Array转换为Set
+let mySet = new Set(myArray);
+
+mySet.has("value1"); // returns true
+
+// 用...(展开操作符)操作符将Set转换为Array
+console.log([...mySet]); // 与myArray完全一致
+</pre>
+
+<h3 id="数组去重">数组去重</h3>
+
+<pre class="brush: js notranslate">// Use to remove duplicate elements from the array
+const numbers = [2,3,4,4,2,3,3,4,4,5,5,6,6,7,5,32,3,4,5]
+console.log([...new Set(numbers)])
+// [2, 3, 4, 5, 6, 7, 32]
+</pre>
+
+<h3 id="String_相关"><code>String</code> 相关</h3>
+
+<pre class="brush: js notranslate">let text = 'India';
+
+let mySet = new Set(text); // Set {'I', 'n', 'd', 'i', 'a'}
+mySet.size; // 5
+
+// 大小写敏感 &amp; duplicate ommision
+new Set("Firefox") // Set(7) [ "F", "i", "r", "e", "f", "o", "x" ]
+new Set("firefox") // Set(6) [ "f", "i", "r", "e", "o", "x" ]
+</pre>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+ <tr>
+ <th scope="col">规范</th>
+ </tr>
+ <tr>
+ <td>{{ SpecName('ESDraft', '#sec-set-objects', 'Set') }}</td>
+ </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</h2>
+
+<div class="hidden">
+<p>The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
+</div>
+
+<p>{{ Compat('javascript.builtins.Set') }}</p>
+
+<h2 id="参见">参见</h2>
+
+<ul>
+ <li>{{ jsxref('Map') }}</li>
+ <li>{{ jsxref('WeakMap') }}</li>
+ <li>{{ jsxref('WeakSet') }}</li>
+</ul>
+
+<p>
+ <audio style="display: none;"></audio>
+</p>