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305 lines
24 KiB
HTML
<article id="wikiArticle">
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<div></div>
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<p> <strong><code>delete</code> 操作符</strong>用于删除对象的某个属性；如果没有指向这个属性的引用，那它最终会被释放。</p>
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<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/expressions-deleteoperator.html" width="100%"></iframe></div>
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<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a class="external" href="https://github.com/mdn/interactive-examples" rel="noopener">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript">delete <em>expression</em>
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</code></pre>
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<p> <em>expression</em> 的计算结果应该是某个属性的引用，例如：</p>
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<pre><code class="language-javascript">delete <em>object.property</em>
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delete <em>object</em>['<em>property</em>']
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</code></pre>
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<h3 id="Parameters" name="Parameters">参数</h3>
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<dl>
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<dt><code>object</code></dt>
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<dd>对象的名称，或计算结果为对象的表达式。</dd>
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</dl>
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<dl>
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<dt><code>property</code></dt>
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<dd>要删除的属性。</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<p>对于所有情况都是<code>true</code>，除非属性是一个自己不可配置的属性，在这种情况下，非严格模式返回 <code>false</code>。</p>
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<h3 id="异常">异常</h3>
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<p>在<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/Strict_mode">严格模式</a>下，如果是属性是一个自己不可配置的属性，会抛出<a href="Reference/Global_objects/SyntaxError" title="SyntaxError 对象代表尝试解析语法上不合法的代码的错误。"><code>Global_objects/SyntaxError</code></a>。</p>
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<h2 id="Description" name="Description">描述</h2>
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<p>与通常的看法不同，<code>delete</code>操作符与直接释放内存<strong>无关</strong>。内存管理 通过断开引用来间接完成的，查看<a href="https://developer.mozilla.org/zh-CNdocs/Web/JavaScript/Memory_Management">内存管理</a>页可了解详情。</p>
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<p><strong><code>delete </code></strong>操作符会从某个对象上移除指定属性。成功删除的时候回返回 <code>true</code>，否则返回 <code>false</code>。但是，以下情况需要重点考虑：</p>
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<ul>
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<li>如果你试图删除的属性不存在，那么delete将不会起任何作用，但仍会返回true</li>
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<li>如果对象的原型链上有一个与待删除属性同名的属性，那么删除属性之后，对象会使用原型链上的那个属性（也就是说，delete操作只会在自身的属性上起作用）</li>
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<li>任何使用 <a href="Reference/Statements/var" title="var 声明语句声明一个变量，并可选地将其初始化为一个值。"><code>var</code></a> 声明的属性不能从全局作用域或函数的作用域中删除。
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<ul>
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<li>这样的话，delete操作不能删除任何在全局作用域中的函数（无论这个函数是来自于函数声明或函数表达式）</li>
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<li>除了在全局作用域中的函数不能被删除，在对象(object)中的函数是能够用delete操作删除的。</li>
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</ul>
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</li>
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<li>任何用<a href="Reference/Statements/let" title="let允许你声明一个作用域被限制在块级中的变量、语句或者表达式。与var关键字不同的是，var声明的变量只能是全局或者整个函数块的。"><code>let</code></a>或<a href="Reference/Statements/const" title="常量是块级作用域，很像使用 let 语句定义的变量。常量的值不能通过重新赋值来改变，并且不能重新声明。"><code>const</code></a>声明的属性不能够从它被声明的作用域中删除。</li>
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<li>不可设置的(Non-configurable)属性不能被移除。这意味着像<a href="Reference/Global_Objects/Math" title="Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。"><code>Math</code></a>, <a href="Reference/Array" title="REDIRECT Array"><code>Array</code></a>, <a href="Reference/Global_Objects/Object" title="Object 构造函数创建一个对象包装器。"><code>Object</code></a>内置对象的属性以及使用<a href="Reference/Global_Objects/Object/defineProperty" title="Object.defineProperty() 方法会直接在一个对象上定义一个新属性，或者修改一个对象的现有属性， 并返回这个对象。"><code>Object.defineProperty()</code></a>方法设置为不可设置的属性不能被删除。</li>
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</ul>
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<p>下面的代码块给出了一个简单的例子：</p>
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<pre><code class="language-javascript">var Employee = {
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age: 28,
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name: 'abc',
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designation: 'developer'
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}
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console.log(delete Employee.name); // returns true
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console.log(delete Employee.age); // returns true
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// 当试着删除一个不存在的属性时
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// 同样会返回true
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console.log(delete Employee.salary); // returns true</code></pre>
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<h3 id="不可配置属性">不可配置属性</h3>
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<p>当一个属性被设置为不可设置，delete操作将不会有任何效果，并且会返回false。在严格模式下会抛出语法错误（<a href="Reference/Global_Objects/SyntaxError" title="SyntaxError 对象代表尝试解析语法上不合法的代码的错误。"><code>SyntaxError</code></a>）。</p>
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<pre><code class="language-javascript">var Employee = {};
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Object.defineProperty(Employee, 'name', {configurable: false});
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console.log(delete Employee.name); // returns false</code></pre>
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<p><a href="Reference/Statements/var" title="var 声明语句声明一个变量，并可选地将其初始化为一个值。"><code>var</code></a>, <a href="Reference/Statements/let" title="let允许你声明一个作用域被限制在块级中的变量、语句或者表达式。与var关键字不同的是，var声明的变量只能是全局或者整个函数块的。"><code>let</code></a>以及<a href="Reference/Statements/const" title="常量是块级作用域，很像使用 let 语句定义的变量。常量的值不能通过重新赋值来改变，并且不能重新声明。"><code>const</code></a>创建的不可设置的属性不能被delete操作删除。</p>
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<pre><code class="language-javascript">var nameOther = 'XYZ';
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// 通过以下方法获取全局属性:
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Object.getOwnPropertyDescriptor(window, 'nameOther');
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// 输出: Object {value: "XYZ",
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// writable: true,
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// enumerable: true,
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// configurable: false}
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// 因为“nameOther”使用var关键词添加，
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// 它被设置为不可设置（non-configurable）
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delete nameOther; // return false</code></pre>
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<p>在严格模式下，这样的操作会抛出异常。</p>
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<h3 id="严格模式与非严格模式的对比"><strong>严格模式与非严格模式的对比</strong></h3>
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<p>在严格模式下，如果对一个变量的直接引用、函数的参数或者函数名使用delete操作，将会抛出语法错误（<a href="Reference/Global_Objects/SyntaxError" title="SyntaxError 对象代表尝试解析语法上不合法的代码的错误。"><code>SyntaxError</code></a>）。</p>
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<p>任何使用var声明的变量都会被标记为不可设置的。在下面的例子中，salary是不可设置的以及不能被删除的。在非严格模式下，下面的delete操作将会返回false。</p>
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<pre><code class="language-javascript">function Employee() {
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delete salary;
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var salary;
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}
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Employee();</code></pre>
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<p>让我们来看看相同的代码在严格模式下会有怎样的表现。会抛出一个语法错误（ <code>SyntaxError）而不是返回false。</code></p>
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<pre><code class="language-javascript">"use strict";
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function Employee() {
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delete salary; // SyntaxError
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var salary;
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}
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// 相似的，任何对任何函数
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// 直接使用delete操作将会抛出语法错误。
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function DemoFunction() {
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//some code
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}
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delete DemoFunction; // SyntaxError</code></pre>
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<h2 id="示例">示例</h2>
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<pre><code class="language-javascript">// 在全局作用域创建 adminName 属性
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adminName = 'xyz';
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// 在全局作用域创建 empCount 属性
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// 因为我们使用了 var，它会标记为不可配置。同样 let 或 const 也是不可配置的。
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var empCount = 43;
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EmployeeDetails = {
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name: 'xyz',
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age: 5,
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designation: 'Developer'
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};
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// adminName 是全局作用域的一个属性。
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// 因为它不是用 var 创建的，所在可以删除。
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// 因此，它是可配置的。
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delete adminName; // 返回 true
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// 相反，empCount 是不可配置的，
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// 因为创建它时使用了 var。
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delete empCount; // 返回 false
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// delete 可用于删除对象的属性
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delete EmployeeDetails.name; // 返回 true
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// 甚至属性不存在，它也会返回 "true"
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delete EmployeeDetails.salary; // 返回 true
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// delete 对内建静态属性不起作用
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delete Math.PI; // 返回 false
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// EmployeeDetails 是全局作用域的一个属性。
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// 因为定义它的时候没有使用 "var"，它被标记为可配置。
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delete EmployeeDetails; // 返回 true
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function f() {
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var z = 44;
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// delete 对局部变量名不起作用
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delete z; // 返回 false
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}</code></pre>
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<h3 id="delete_和原型链"><code>delete</code> 和原型链</h3>
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<p>在下面的示例中，我们删除一个对象的自己的属性，而原型链上具有相同名称的属性可用：</p>
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<pre><code class="language-javascript">function Foo() {
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this.bar = 10;
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}
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Foo.prototype.bar = 42;
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var foo = new Foo();
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// 返回 true，因为删除的是 foo 对象的自身属性
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delete foo.bar;
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// foo.bar 仍然可用，因为它在原型链上可用。
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console.log(foo.bar);
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// 从原型上删除属性
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delete Foo.prototype.bar;
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// 输出 "undefined"，因为不能继承这个属性了
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console.log(foo.bar);
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</code></pre>
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<h3 id="Deleting_array_elements" name="Deleting_array_elements">删除数组元素</h3>
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<p>当你删除一个数组元素时，数组的长度不受影响。即便你删除了数组的最后一个元素也是如此。</p>
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<p>当用 <code>delete</code> 操作符删除一个数组元素时，被删除的元素已经不再属于该数组。下面的例子中用 <code>delete </code>删除了<code> trees[3]</code>。</p>
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<pre><code class="language-javascript">var trees = ["redwood","bay","cedar","oak","maple"];
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delete trees[3];
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if (3 in trees) {
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// 这里不会执行
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}
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</code></pre>
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<p>如果你想让一个数组元素继续存在但是其值是 <code>undefined</code>，那么可以使用将 <code>undefined</code> 赋值给这个元素而不是使用 <code>delete</code>。下面的例子中，trees[3] 被赋值为 <code>undefined</code>，但该元素仍然存在。</p>
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<pre><code class="language-javascript">var trees = ["redwood","bay","cedar","oak","maple"];
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trees[3] = undefined;
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if (3 in trees) {
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// 这里会被执行
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}</code></pre>
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<p>如果你想通过改变数组的内容来移除一个数组元素，请使用<code><a href="Reference/Global_Objects/Array/splice" title="splice() 方法通过删除或替换现有元素来修改数组,并以数组形式返回被修改的内容。此方法会改变原数组。"><code>splice</code></a></code>方法。在下面的例子中，通过使用<code><a href="Reference/Global_Objects/Array/splice" title="splice() 方法通过删除或替换现有元素来修改数组,并以数组形式返回被修改的内容。此方法会改变原数组。"><code>splice</code></a></code>，将trees[3]从数组中移除。</p>
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<pre><code class="language-javascript">var trees = ['redwood', 'bay', 'cedar', 'oak', 'maple'];
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trees.splice(3,1);
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console.log(trees); // ["redwood", "bay", "cedar", "maple"]</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">Specification</th>
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<th scope="col">Status</th>
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<th scope="col">Comment</th>
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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-delete-operator" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">The delete Operator</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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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-delete-operator" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">The delete Operator</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-262/5.1/#sec-11.4.1" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">The delete Operator</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/publications/files/ECMA-ST-ARCH/ECMA-262,%201st%20edition,%20June%201997.pdf#sec-11.4.1" hreflang="en" lang="en" rel="noopener">ECMAScript 1st Edition (ECMA-262)<br/><small lang="zh-CN">The delete Operator</small></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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</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 on 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>delete</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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Yes</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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Yes</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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Yes</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>
|
||
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">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
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">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
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">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
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">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td></tr><tr><th scope="row">Temporal dead zone</th><td class="bc-supports-unknown bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></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">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
36</td><td class="bc-supports-unknown bc-browser-ie"><span class="bc-browser-name">IE</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></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">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
36</td><td class="bc-supports-unknown bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-unknown bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></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">
|
||
<abbr class="bc-level bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
|
||
</abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-unknown bc-supports">
|
||
<abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown">
|
||
<span>Compatibility unknown</span>
|
||
|
||
</abbr></span></dt><dd>Compatibility unknown</dd></dl></section></div><p></p>
|
||
<h2 id="跨浏览器提示">跨浏览器提示</h2>
|
||
<p>尽管ECMAScript使得对象的迭代顺序依赖于实现，但似乎所有主流浏览器都支持基于最早添加的属性（至少对于不在原型上的属性）的迭代顺序（译注：ES5 标准取消了属性遍历的顺序的规定）。但是，在 IE 中，使用 <code>delete</code> 删除一个属性后，奇怪的事情发生了，如果被删除的属性重新被添加，那么遍历时，该属性的顺序会是上次删除前的那个位置所应该有的顺序,而不是出现在遍历的最后一个。</p>
|
||
<p>如果你想让对象的遍历顺序兼容所有的浏览器，那么你可以使用两个数组来模拟 (一个做为keys，一个做为 values)， 或者建立<span class="short_text" id="result_box" lang="zh-CN"><span>一个</span><span>由单一</span><span>属性</span><span>的</span><span>对象组成的</span><span>数组</span></span>等。</p>
|
||
<h2 id="See_also" name="See_also">参见</h2>
|
||
<ul>
|
||
<li><a class="external" href="http://perfectionkills.com/understanding-delete/" rel="noopener">深入分析 delete</a></li>
|
||
<li><a href="Reference/Global_Objects/Reflect/deleteProperty" title="静态方法 Reflect.deleteProperty() 允许用于删除属性。它很像 delete operator ，但它是一个函数。"><code>Reflect.deleteProperty()</code></a></li>
|
||
<li><a href="Reference/Global_Objects/Map/delete" title=" delete() 方法用于移除 Map 对象中指定的元素。"><code>Map.prototype.delete()</code></a></li>
|
||
</ul>
|
||
</article> |