path: root/files/zh-tw/web/javascript/reference/global_objects/set/index.html

---
title: Set
slug: Web/JavaScript/Reference/Global_Objects/Set
tags:
  - ECMAScript 2015
  - Global Objects
  - JavaScript
  - Object
  - set
translation_of: Web/JavaScript/Reference/Global_Objects/Set
---
<div>{{JSRef}}</div>

<p><strong><code>Set</code></strong> 物件可讓你儲存任何類型的唯一值（unique），不論是{{Glossary("Primitive", "基本型別（primitive）值")}}或物件參考（references）。</p>

<div>{{EmbedInteractiveExample("pages/js/set-prototype-constructor.html")}}</div>



<h2 id="語法">語法</h2>

<pre class="syntaxbox notranslate">new Set([<em>iterable</em>]);</pre>

<h3 id="參數">參數</h3>

<dl>
 <dt><code>iterable</code></dt>
 <dd>若一個<a href="/zh-TW/docs/Web/JavaScript/Reference/Statements/for...of">可迭代物件</a>被傳入，其所有的元素將會被加入至新的 <code>Set</code>。若你沒有指定此參數，或參數值為 <code>null</code>，則新的 <code>Set</code> 會是空的。</dd>
</dl>

<h3 id="回傳值">回傳值</h3>

<p>一個新的 <code>Set</code> 物件。</p>

<h2 id="描述">描述</h2>

<p><code>Set</code> 對象是數值的收集器。您可以按插入順序迭代收集器中的元素。在 <code>Set</code> 裡的元素只會出現一次<strong>；</strong> 意即在<code>Set</code>裡的元素都是獨一無二</p>

<h3 id="值的相等性">值的相等性</h3>

<p>因為在 Set 裡每個值都是獨立的，所以都會檢查值的相等性。在早期的ECMAScript規範版本中，此處算法跟基於===操作符中使用的算法並不相同。具體來說，在 <code>Set</code>裡+0(在嚴格模式是和-0相等)和-0是不同的值。然而在 ECMAScript 2015規範中這點已被更改。請參閱 <a href="#Browser_compatibility">瀏覽器兼容性</a> 中的"Value equality for -0 and 0"。</p>

<p>另外，NaN和undefined都可以被放置在Set 中， NaN之間被視為相同的值（儘管 NaN !== NaN）。</p>

<dl>
 <dt><code>Set.length</code></dt>
 <dd>The value of the <code>length</code> property is 0.</dd>
 <dt>{{jsxref("Set.@@species", "get Set[@@species]")}}</dt>
 <dd>The constructor function that is used to create derived objects.</dd>
 <dt>{{jsxref("Set.prototype")}}</dt>
 <dd>Represents the prototype for the <code>Set</code> constructor. Allows the addition of properties to all <code>Set</code> objects.</dd>
</dl>

<h2 id="Set_物件實體"><code>Set</code> 物件實體</h2>

<p>All <code>Set</code> instances inherit from {{jsxref("Set.prototype")}}.</p>

<h3 id="屬性">屬性</h3>

<p>{{page('en-US/Web/JavaScript/Reference/Global_Objects/Set/prototype','Properties')}}</p>

<h3 id="方法">方法</h3>

<p>{{page('en-US/Web/JavaScript/Reference/Global_Objects/Set/prototype','Methods')}}</p>

<h2 id="範例">範例</h2>

<h3 id="使用_Set_物件">使用 <code>Set</code> 物件</h3>

<pre class="brush: js notranslate">var 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' ]
var o = {a: 1, b: 2};
mySet.add(o);

mySet.add({a: 1, b: 2}); // o is referencing a different object so this is okay

mySet.has(1); // true
mySet.has(3); // false, 3 has not been added to the set
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); // removes 5 from the set
mySet.has(5);    // false, 5 has been removed

mySet.size; // 4, we just removed one value
console.log(mySet);// Set [ 1, "some text", Object {a: 1, b: 2}, Object {a: 1, b: 2} ]</pre>

<h3 id="迭代_Sets">迭代 Sets</h3>

<pre class="brush: js notranslate">// iterate over items in set
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet) console.log(item);

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet.keys()) console.log(item);

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet.values()) console.log(item);

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
//(key and value are the same here)
for (let [key, value] of mySet.entries()) console.log(key);

// convert Set object to an Array object, with <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from">Array.from</a>
var myArr = Array.from(mySet); // [1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}]

// the following will also work if run in an HTML document
mySet.add(document.body);
mySet.has(document.querySelector('body')); // true

// converting between Set and Array
mySet2 = new Set([1, 2, 3, 4]);
mySet2.size; // 4
[...mySet2]; // [1, 2, 3, 4]

// intersect can be simulated via
var intersection = new Set([...set1].filter(x =&gt; set2.has(x)));

// difference can be simulated via
var difference = new Set([...set1].filter(x =&gt; !set2.has(x)));

// Iterate set entries with forEach
mySet.forEach(function(value) {
  console.log(value);
});

// 1
// 2
// 3
// 4</pre>

<h3 id="實作基本的_set_操作">實作基本的 set 操作</h3>

<pre class="brush: js notranslate">Set.prototype.isSuperset = function(subset) {
    for (var elem of subset) {
        if (!this.has(elem)) {
            return false;
        }
    }
    return true;
}

Set.prototype.union = function(setB) {
    var union = new Set(this);
    for (var elem of setB) {
        union.add(elem);
    }
    return union;
}

Set.prototype.intersection = function(setB) {
    var intersection = new Set();
    for (var elem of setB) {
        if (this.has(elem)) {
            intersection.add(elem);
        }
    }
    return intersection;
}

Set.prototype.difference = function(setB) {
    var difference = new Set(this);
    for (var elem of setB) {
        difference.delete(elem);
    }
    return difference;
}

//Examples
var setA = new Set([1, 2, 3, 4]),
    setB = new Set([2, 3]),
    setC = new Set([3, 4, 5, 6]);

setA.isSuperset(setB); // =&gt; true
setA.union(setC); // =&gt; Set [1, 2, 3, 4, 5, 6]
setA.intersection(setC); // =&gt; Set [3, 4]
setA.difference(setC); // =&gt; Set [1, 2]

</pre>

<h3 id="與_Array_物件關聯">與 <code>Array</code> 物件關聯</h3>

<pre class="brush: js notranslate">var myArray = ['value1', 'value2', 'value3'];

// Use the regular Set constructor to transform an Array into a Set
var mySet = new Set(myArray);

mySet.has('value1'); // returns true

// Use the spread operator to transform a set into an Array.
console.log([...mySet]); // Will show you exactly the same Array as myArray</pre>

<h3 id="與_Strings_關聯">與 <code>Strings</code> 關聯</h3>

<pre class="brush: js notranslate">var text = 'India';

var mySet = new Set(text);  // Set ['I', 'n', 'd', 'i', 'a']
mySet.size;  // 5
</pre>

<h2 id="規範">規範</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-set-objects', 'Set')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td>Initial definition.</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-set-objects', 'Set')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="瀏覽器相容性">瀏覽器相容性</h2>



<p>{{Compat("javascript.builtins.Set")}}</p>

<h2 id="參見">參見</h2>

<ul>
 <li>{{jsxref("Map")}}</li>
 <li>{{jsxref("WeakMap")}}</li>
 <li>{{jsxref("WeakSet")}}</li>
</ul>