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132 lines
11 KiB
HTML
<article id="wikiArticle">
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<p></p><p></p>
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<p><strong><code>unshift()</code></strong> 方法将一个或多个元素添加到数组的开头，并返回该数组的新长度。</p>
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<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/array-unshift.html" width="100%"></iframe></div>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript">arr.unshift(element1, ..., elementN)
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</code></pre>
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<h3 id="Parameters" name="Parameters">参数列表</h3>
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<dl>
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<dt><code>elementN</code></dt>
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<dd>要添加到数组开头的元素。</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<p>当一个对象调用该方法时，返回其 <a href="Reference/Global_Objects/Array/length" title="length 是Array的实例属性。返回或设置一个数组中的元素个数。该值是一个无符号 32-bit 整数，并且总是大于数组最高项的下标。"><code>length</code></a> 属性值。</p>
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<dl>
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</dl>
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<h2 id="Description" name="Description">描述</h2>
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<p><code>unshift</code> 方法会在调用它的类数组对象的开始位置插入给定的参数。</p>
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<p><code>unshift</code> 特意被设计成具有通用性；这个方法能够通过 <a href="Reference/Global_Objects/Function/call" title="call() 方法调用一个函数, 其具有一个指定的this值和分别地提供的参数(参数的列表)。"><code>call</code></a> 或 <a href="Reference/Global_Objects/Function/apply" title="apply() 方法调用一个具有给定this值的函数，以及作为一个数组（或类似数组对象）提供的参数。"><code>apply</code></a> 方法作用于类数组对象上。<span style="line-height: inherit;">不过对于没有 length 属性（代表从0开始的一系列连续的数字属性的最后一个）的对象，调用该方法可能没有任何意义。</span></p>
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<p>Please note that, if multiple elements are passed as parameters, they're inserted in chunk at the beginning of the object, in the exact same order they were passed as parameters. Hence, calling unshift with <strong>n</strong> arguments <strong>once</strong>, or calling it <strong>n</strong> times with <strong>1</strong> argument (with a loop, for example), don't yield the same results. See example:</p>
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<pre><code class="language-javascript">let arr = [4,5,6];
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arr.unshift(1,2,3);
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console.log(arr); // [<strong>1, 2, 3</strong>, 4, 5, 6]
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arr = [4,5,6]; // resetting the array
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arr.unshift(1);
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arr.unshift(2);
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arr.unshift(3);
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console.log(arr); // [<strong>3, 2, 1</strong>, 4, 5, 6]
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</code></pre>
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<h2 id="示例">示例</h2>
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<pre><code class="language-javascript">let arr = [1, 2];
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arr.unshift(0); // result of the call is 3, which is the new array length
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// arr is [0, 1, 2]
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arr.unshift(-2, -1); // the new array length is 5
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// arr is [-2, -1, 0, 1, 2]
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arr.unshift([-4, -3]); // the new array length is 6
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// arr is [[-4, -3], -2, -1, 0, 1, 2]
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arr.unshift([-7, -6], [-5]); // the new array length is 8
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// arr is [ [-7, -6], [-5], [-4, -3], -2, -1, 0, 1, 2 ]
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</code></pre>
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<h2 id="规范">规范</h2>
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<table class="standard-table">
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<tbody>
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<tr>
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<th scope="col">规范</th>
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<th scope="col">状态</th>
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<th scope="col">备注</th>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf" hreflang="en" lang="en" rel="noopener" title="ECMAScript 3rd Edition (ECMA-262)">ECMAScript 3rd Edition (ECMA-262)</a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>Initial definition. Implemented in JavaScript 1.2.</td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.13" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Array.prototype.unshift</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.unshift" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Array.prototype.unshift</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td> </td>
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</tr>
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<tr>
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<td><a class="external" href="https://tc39.github.io/ecma262/#sec-array.prototype.unshift" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Array.prototype.unshift</small></a></td>
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<td><span class="spec-Draft">Draft</span></td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<h2 id="浏览器兼容性">浏览器兼容性</h2>
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<div class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>
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<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row"><code>unshift</code></th><td class="bc-supports-yes bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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1</td><td class="bc-supports-yes bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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12</td><td class="bc-supports-yes bc-browser-firefox"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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1</td><td class="bc-supports-yes bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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5.5</td><td class="bc-supports-yes bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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4</td><td class="bc-supports-yes bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</td></tr></tbody></table><section class="bc-legend" id="sect1"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
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<abbr class="bc-level bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr></span></dt><dd>Full support</dd></dl></section></div><p></p>
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<h2 id="参见">参见</h2>
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<ul>
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<li><a href="Reference/Global_Objects/Array/push" title="push() 方法将一个或多个元素添加到数组的末尾，并返回该数组的新长度。"><code>Array.prototype.push()</code></a></li>
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<li><a href="Reference/Global_Objects/Array/pop" title="pop()方法从数组中删除最后一个元素，并返回该元素的值。此方法更改数组的长度。"><code>Array.prototype.pop()</code></a></li>
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<li><a href="Reference/Global_Objects/Array/shift" title="shift() 方法从数组中删除第一个元素，并返回该元素的值。此方法更改数组的长度。"><code>Array.prototype.shift()</code></a></li>
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<li><a href="Reference/Global_Objects/Array/concat" title="concat() 方法用于合并两个或多个数组。此方法不会更改现有数组，而是返回一个新数组。"><code>Array.prototype.concat()</code></a></li>
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</ul>
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</article> |