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author | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
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committer | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
commit | 33058f2b292b3a581333bdfb21b8f671898c5060 (patch) | |
tree | 51c3e392513ec574331b2d3f85c394445ea803c6 /files/zh-cn/web/javascript/reference/global_objects/array/unshift/index.html | |
parent | 8b66d724f7caf0157093fb09cfec8fbd0c6ad50a (diff) | |
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diff --git a/files/zh-cn/web/javascript/reference/global_objects/array/unshift/index.html b/files/zh-cn/web/javascript/reference/global_objects/array/unshift/index.html new file mode 100644 index 0000000000..7b1148813f --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/array/unshift/index.html @@ -0,0 +1,120 @@ +--- +title: Array.prototype.unshift() +slug: Web/JavaScript/Reference/Global_Objects/Array/unshift +tags: + - Array + - JavaScript + - Method + - 原型 + - 参考资料 + - 数组 + - 方法 +translation_of: Web/JavaScript/Reference/Global_Objects/Array/unshift +--- +<p>{{JSRef}}</p> + +<p><strong><code>unshift()</code></strong> 方法将一个或多个元素添加到数组的<strong>开头</strong>,并返回该数组的<strong>新长度(该</strong>方法修改原有数组<strong>)</strong>。</p> + +<div>{{EmbedInteractiveExample("pages/js/array-unshift.html")}}</div> + +<h2 id="Syntax" name="Syntax">语法</h2> + +<pre class="syntaxbox">arr.unshift(element1, ..., elementN) +</pre> + +<h3 id="Parameters" name="Parameters">参数列表</h3> + +<dl> + <dt><code>elementN</code></dt> + <dd>要添加到数组开头的元素或多个元素。</dd> +</dl> + +<h3 id="返回值">返回值</h3> + +<p>当一个对象调用该方法时,返回其 {{jsxref("Array.length", "length")}} 属性值。</p> + +<dl> +</dl> + +<h2 id="Description" name="Description">描述</h2> + +<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> + +<p><code>unshift</code> 特意被设计成具有通用性;这个方法能够通过 {{jsxref("Function.call", "call")}} 或 {{jsxref("Function.apply", "apply")}} 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> + +<p>注意, 如果传入多个参数,它们会被以块的形式插入到对象的开始位置,它们的顺序和被作为参数传入时的顺序一致。 于是,传入多个参数调用一次 <code>unshift</code> ,和传入一个参数调用多次 <code>unshift</code> (例如,循环调用),它们将得到不同的结果。例如:</p> + +<pre class="syntaxbox">let arr = [4,5,6]; +arr.unshift(1,2,3); +console.log(arr); // [<strong>1, 2, 3</strong>, 4, 5, 6] + +arr = [4,5,6]; // 重置数组 +arr.unshift(1); +arr.unshift(2); +arr.unshift(3); +console.log(arr); // [<strong>3, 2, 1</strong>, 4, 5, 6] +</pre> + +<h2 id="示例">示例</h2> + +<pre class="brush: js">let arr = [1, 2]; + +arr.unshift(0); // result of the call is 3, which is the new array length +// arr is [0, 1, 2] + +arr.unshift(-2, -1); // the new array length is 5 +// arr is [-2, -1, 0, 1, 2] + +arr.unshift([-4, -3]); // the new array length is 6 +// arr is [[-4, -3], -2, -1, 0, 1, 2] + +arr.unshift([-7, -6], [-5]); // the new array length is 8 +// arr is [ [-7, -6], [-5], [-4, -3], -2, -1, 0, 1, 2 ] +</pre> + +<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('ES3')}}</td> + <td>{{Spec2('ES3')}}</td> + <td>Initial definition. Implemented in JavaScript 1.2.</td> + </tr> + <tr> + <td>{{SpecName('ES5.1', '#sec-15.4.4.13', 'Array.prototype.unshift')}}</td> + <td>{{Spec2('ES5.1')}}</td> + <td></td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-array.prototype.unshift', 'Array.prototype.unshift')}}</td> + <td>{{Spec2('ES6')}}</td> + <td></td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-array.prototype.unshift', 'Array.prototype.unshift')}}</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> + +<div class="hidden">兼容性表是使用结构化数据生成的. 如果您希望为此数据做贡献, 请检出(check out) <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> 同时向我们提交一个pull request.</div> + +<p>{{Compat("javascript.builtins.Array.unshift")}}</p> + +<h2 id="参见">参见</h2> + +<ul> + <li>{{jsxref("Array.prototype.push()")}}</li> + <li>{{jsxref("Array.prototype.pop()")}}</li> + <li>{{jsxref("Array.prototype.shift()")}}</li> + <li>{{jsxref("Array.prototype.concat()")}}</li> +</ul> |