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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 &gt;&gt;&gt; 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 &lt; 0,
+      //  a. Let k be len + n.
+      //  b. If k &lt; 0, let k be 0.
+      var k = Math.max(n &gt;= 0 ? n : len - Math.abs(n), 0);
+
+      function sameValueZero(x, y) {
+        return x === y || (typeof x === 'number' &amp;&amp; typeof y === 'number' &amp;&amp; isNaN(x) &amp;&amp; isNaN(y));
+      }
+
+      // 7. Repeat, while k &lt; len
+      while (k &lt; 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>