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---
title: Array.prototype.includes()
slug: Web/JavaScript/Reference/Global_Objects/Array/includes
tags:
- Array
- JavaScript
- Method
- Prototype
- Reference
- polyfill
translation_of: Web/JavaScript/Reference/Global_Objects/Array/includes
---
<div>{{JSRef}}</div>
<p><code><strong>includes()</strong></code> 方法會判斷陣列是否包含特定的元素，並以此來回傳 <code>true</code> 或 <code>false</code>。</p>
<div>{{EmbedInteractiveExample("pages/js/array-includes.html")}}</div>
<h2 id="語法">語法</h2>
<pre class="syntaxbox"><var>arr</var>.includes(<var>searchElement[</var>, <var>fromIndex]</var>)
</pre>
<h3 id="參數">參數</h3>
<dl>
<dt><code>searchElement</code></dt>
<dd>要搜尋的元素。</dd>
<dt><code>fromIndex</code> {{optional_inline}}</dt>
<dd>要於此陣列中開始搜尋 <code>searchElement</code> 的位置。如為負數值，則自 <code>array.length + fromIndex</code> 開始向後搜尋。預設值為 0。</dd>
</dl>
<h3 id="回傳值">回傳值</h3>
<p>布林值（{{jsxref("Boolean")}}）。</p>
<h2 id="範例">範例</h2>
<pre class="brush: js">[1, 2, 3].includes(2); // true
[1, 2, 3].includes(4); // false
[1, 2, 3].includes(3, 3); // false
[1, 2, 3].includes(3, -1); // true
[1, 2, NaN].includes(NaN); // true
</pre>
<h3 id="fromIndex_大於或等於陣列長度"><code>fromIndex</code> 大於或等於陣列長度</h3>
<p>如果 <code>fromIndex</code>大於或等於陣列長度, 會回傳<code>false</code>. 此陣列將不會被搜尋.</p>
<pre class="brush: js">var arr = ['a', 'b', 'c'];
arr.includes('c', 3); // false
arr.includes('c', 100); // false</pre>
<h3 id="Computed_index_is_less_than_0">Computed index is less than 0</h3>
<p>If <code>fromIndex</code> is negative, the computed index is calculated to be used as a position in the array at which to begin searching for <code>searchElement</code>. If the computed index is less than 0, the entire array will be searched.</p>
<pre class="brush: js">// array length is 3
// fromIndex is -100
// computed index is 3 + (-100) = -97
var arr = ['a', 'b', 'c'];
arr.includes('a', -100); // true
arr.includes('b', -100); // true
arr.includes('c', -100); // true</pre>
<h3 id="includes_used_as_a_generic_method"><code>includes()</code> used as a generic method</h3>
<p><code>includes()</code> method is intentionally generic. It does not require <code>this</code> value to be an Array object, so it can be applied to other kinds of objects (e.g. array-like objects). The example below illustrates <code>includes()</code> method called on the function's <a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments">arguments</a> object.</p>
<pre class="brush: js">(function() {
console.log([].includes.call(arguments, 'a')); // true
console.log([].includes.call(arguments, 'd')); // false
})('a','b','c');</pre>
<h2 id="Polyfill">Polyfill</h2>
<pre class="brush: js">// https://tc39.github.io/ecma262/#sec-array.prototype.includes
if (!Array.prototype.includes) {
Object.defineProperty(Array.prototype, 'includes', {
value: function(searchElement, fromIndex) {
if (this == null) {
throw new TypeError('"this" is null or not defined');
}
// 1. Let O be ? ToObject(this value).
var o = Object(this);
// 2. Let len be ? ToLength(? Get(O, "length")).
var len = o.length >>> 0;
// 3. If len is 0, return false.
if (len === 0) {
return false;
}
// 4. Let n be ? ToInteger(fromIndex).
// (If fromIndex is undefined, this step produces the value 0.)
var n = fromIndex | 0;
// 5. If n ≥ 0, then
// a. Let k be n.
// 6. Else n < 0,
// a. Let k be len + n.
// b. If k < 0, let k be 0.
var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);
function sameValueZero(x, y) {
return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
}
// 7. Repeat, while k < len
while (k < len) {
// a. Let elementK be the result of ? Get(O, ! ToString(k)).
// b. If SameValueZero(searchElement, elementK) is true, return true.
if (sameValueZero(o[k], searchElement)) {
return true;
}
// c. Increase k by 1.
k++;
}
// 8. Return false
return false;
}
});
}
</pre>
<p>If you need to support truly obsolete JavaScript engines that don't support <code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty">Object.defineProperty</a></code>, it's best not to polyfill <code>Array.prototype</code> methods at all, as you can't make them non-enumerable.</p>
<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('ES7', '#sec-array.prototype.includes', 'Array.prototype.includes')}}</td>
<td>{{Spec2('ES7')}}</td>
<td>Initial definition.</td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-array.prototype.includes', 'Array.prototype.includes')}}</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>
<div>
<p>{{Compat("javascript.builtins.Array.includes")}}</p>
</div>
<h2 id="參見">參見</h2>
<ul>
<li>{{jsxref("TypedArray.prototype.includes()")}}</li>
<li>{{jsxref("String.prototype.includes()")}}</li>
<li>{{jsxref("Array.prototype.indexOf()")}}</li>
<li>{{jsxref("Array.prototype.find()")}}</li>
<li>{{jsxref("Array.prototype.findIndex()")}}</li>
</ul>
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