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diff --git a/files/zh-cn/web/javascript/reference/global_objects/array/includes/index.html b/files/zh-cn/web/javascript/reference/global_objects/array/includes/index.html new file mode 100644 index 0000000000..183d9978b3 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/array/includes/index.html @@ -0,0 +1,185 @@ +--- +title: Array.prototype.includes() +slug: Web/JavaScript/Reference/Global_Objects/Array/includes +tags: + - Array + - ECMAScript 2016 + - JavaScript + - 数组 + - 方法 +translation_of: Web/JavaScript/Reference/Global_Objects/Array/includes +--- +<div>{{JSRef}} </div> + +<p><code><strong>includes()</strong></code> 方法用来判断一个数组是否包含一个指定的值，根据情况，如果包含则返回 true，否则返回false。</p> + +<div>{{EmbedInteractiveExample("pages/js/array-includes.html")}}</div> + + + +<h2 id="语法">语法</h2> + +<pre><var>arr</var>.includes(<var>valueToFind[</var>, <var>fromIndex]</var>)</pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>valueToFind</code></dt> + <dd> + <p>需要查找的元素值。</p> + + <div class="blockIndicator note"> + <p><strong>Note: </strong>使用<strong> </strong><code>includes()</code>比较字符串和字符时是区分大小写。</p> + </div> + </dd> + <dt><code>fromIndex</code> {{optional_inline}}</dt> + <dd>从<code>fromIndex</code> 索引处开始查找 <code>valueToFind</code>。如果为负值，则按升序从 <code>array.length + fromIndex</code> 的索引开始搜 （即使从末尾开始往前跳 <code>fromIndex</code> 的绝对值个索引，然后往后搜寻）。默认为 0。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p>A {{jsxref("Boolean")}} which is <code>true</code> if the value <code>valueToFind</code> is found within the array (or the part of the array indicated by the index <code>fromIndex</code>, if specified). Values of zero are all considered to be equal regardless of sign (that is, -0 is considered to be equal to both 0 and +0), but <code>false</code> is not considered to be the same as 0.</p> + +<p>返回一个布尔值 {{jsxref("Boolean")}} ，如果在数组中找到了（如果传入了 <code>fromIndex</code> ，表示在 <code>fromIndex</code> 指定的索引范围中找到了）则返回 <code>true</code> 。</p> + +<div class="note"> +<p><strong>Note:</strong> Technically speaking, <code>includes()</code> uses the <code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness#Same-value-zero_equality">sameValueZero</a></code> algorithm to determine whether the given element is found.</p> +</div> + +<h2 id="示例">示例</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_大于等于数组长度">fromIndex 大于等于数组长度</h3> + +<p>如果 <code>fromIndex</code> 大于等于数组的长度，则会返回 <code>false</code>，且该数组不会被搜索。</p> + +<pre class="brush: js">var arr = ['a', 'b', 'c']; + +arr.includes('c', 3); // false +arr.includes('c', 100); // false</pre> + +<h3 id="计算出的索引小于_0">计算出的索引小于 0</h3> + +<p>如果 <code>fromIndex </code>为负值，计算出的索引将作为开始搜索<code>searchElement</code>的位置。如果计算出的索引小于 0，则整个数组都会被搜索。</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 +arr.includes('a', -2); // false</pre> + +<h3 id="作为通用方法的_includes">作为通用方法的 includes()</h3> + +<p><code>includes()</code> 方法有意设计为通用方法。它不要求<code>this</code>值是数组对象，所以它可以被用于其他类型的对象 (比如类数组对象)。下面的例子展示了 在函数的 <a href="/zh-CN/docs/Web/JavaScript/Reference/Functions/arguments">arguments</a> 对象上调用的 <code>includes()</code> 方法。</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(valueToFind, 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(valueToFind, elementK) is true, return true. + if (sameValueZero(o[k], valueToFind)) { + return true; + } + // c. Increase k by 1. + k++; + } + + // 8. Return false + return false; + } + }); +} + +</pre> + +<p>如果你需要支持那些不支持<code><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty">Object.defineProperty</a></code>的废弃JavaScript 引擎，你最好不要 polyfill <code>Array.prototype</code> 方法，因为你不能使它们不可枚举。</p> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">规范</th> + <th scope="col">状态</th> + <th scope="col">备注</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="浏览器兼容性">浏览器兼容性</h2> + + + +<p>{{Compat("javascript.builtins.Array.includes")}}</p> + +<h2 id="参见">参见</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> |