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54 lines
5.0 KiB
HTML
<article id="wikiArticle">
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<div></div>
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<h2 id="错误提示">错误提示</h2>
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<pre class="syntaxbox">TypeError: can't delete non-configurable array element (Firefox)
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TypeError: Cannot delete property '2' of [object Array] (Chrome)
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</pre>
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<h2 id="错误类型">错误类型</h2>
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<p><a href="Reference/Global_Objects/TypeError" title="TypeError（类型错误） 对象用来表示值的类型非预期类型时发生的错误。"><code>TypeError</code></a></p>
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<h2 id="哪里出错了？">哪里出错了？</h2>
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<p>这个错误提示发生于当试图<a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length#Shortening_an_array">缩短一个数组的长度</a>的时候，其中有元素是不可配置的（<a href="/en-US/docs/Web/JavaScript/Data_structures#Properties">non-configurable</a>）。正常情况下，缩短数组的长度，则超出限度的元素会被删除，而这里指的是这种操作失效的情况。</p>
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<p><code><font face="Open Sans, arial, x-locale-body, sans-serif"> </font>configurable</code> 特性控制着属性是否可以从对象中删除，以及它的特性（除了 writable 之外）是否可以发生改变。</p>
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<p>通常，使用<a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#Syntax">数组初始化语句</a>创建的对象是可配置的，而通过 <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> 创建的属性，默认则是不可配置的。</p>
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<h2 id="示例">示例</h2>
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<h3 id="通过_Object.defineProperty_创建的不可配置属性"><code><font face="x-locale-heading-primary, zillaslab, Palatino, Palatino Linotype, x-locale-heading-secondary, serif">通过 </font>Object.defineProperty 创建的不可配置属性</code></h3>
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<p>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> 且在没有明确将属性设定为可配置的情况下，默认可以创建不可配置属性。</p>
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<pre class="brush: js example-bad">var arr = [];
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Object.defineProperty(arr, 0, {value: 0});
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Object.defineProperty(arr, 1, {value: "1"});
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arr.length = 1;
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// TypeError: can't delete non-configurable array element
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</pre>
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<p>如果想要缩短数组长度的话，需要将其中的元素设置为可配置的。</p>
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<pre class="brush: js example-good">var arr = [];
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Object.defineProperty(arr, 0, {value: 0, configurable: true});
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Object.defineProperty(arr, 1, {value: "1", configurable: true});
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arr.length = 1;
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</pre>
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<h3 id="密封的数组"><code>密封的数组</code></h3>
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<p> <a href="Reference/Global_Objects/Object/seal" title="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 https://github.com/mdn/interactive-examples and send us a pull request."><code>Object.seal()</code></a> 函数会将数组中现存的所有元素标记为不可配置。</p>
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<pre class="brush: js example-bad">var arr = [1,2,3];
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Object.seal(arr);
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arr.length = 1;
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// TypeError: can't delete non-configurable array element
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</pre>
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<p>（为了解决上述问题，）或者是移除 <a href="Reference/Global_Objects/Object/seal" title="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 https://github.com/mdn/interactive-examples and send us a pull request."><code>Object.seal()</code></a> 调用，或者将数组拷贝一份。在拷贝数组的情况下，缩短备份数组的长度并不会修改原始数组的长度。</p>
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<pre class="brush: js example-good">var arr = [1,2,3];
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Object.seal(arr);
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// Copy the initial array to shorten the copy
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var copy = Array.from(arr);
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copy.length = 1;
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// arr.length == 3
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</pre>
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<h2 id="相关内容">相关内容</h2>
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<ul>
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<li><a href="/en-US/docs/Web/JavaScript/Data_structures#Properties">[[Configurable]]</a></li>
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<li><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>Array.length</code></a></li>
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<li><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></li>
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<li><a href="Reference/Global_Objects/Object/seal" title="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 https://github.com/mdn/interactive-examples and send us a pull request."><code>Object.seal()</code></a></li>
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</ul>
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</article> |