uTools-Manuals/docs/javascript/Reference/Global_Objects/Object/keys.html

<article id="wikiArticle">
<p></p><p></p>
<p><code><strong>Object.keys()</strong></code> 方法会返回一个由一个给定对象的自身可枚举属性组成的数组，数组中属性名的排列顺序和使用<font face="Consolas, Liberation Mono, Courier, monospace"> </font><a href="Reference/Statements/for...in" title="for...in语句以任意顺序遍历一个对象的可枚举属性。对于每个不同的属性，语句都会被执行。"><code>for...in</code></a> 循环遍历该对象时返回的顺序一致 。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code>Object.keys(<var>obj</var>)</code></code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt>obj</dt>
<dd>要返回其枚举自身属性的对象。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>一个表示给定对象的所有可枚举属性的字符串数组。</p>
<h2 id="Description" name="Description" style="margin-bottom: 20px; line-height: 30px;">描述</h2>
<p><code>Object.keys</code> 返回一个所有元素为字符串的数组，其元素来自于从给定的<code>object</code>上面可直接枚举的属性。这些属性的顺序与手动遍历该对象属性时的一致。</p>
<h2 id="例子">例子</h2>
<pre><code  class="language-javascript">// simple array
var arr = ['a', 'b', 'c'];
console.log(Object.keys(arr)); // console: ['0', '1', '2']

// array like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.keys(obj)); // console: ['0', '1', '2']

// array like object with random key ordering
var anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.keys(anObj)); // console: ['2', '7', '100']

// getFoo is a property which isn't enumerable
var myObj = Object.create({}, {
  getFoo: {
    value: function () { return this.foo; }
  } 
});
myObj.foo = 1;
console.log(Object.keys(myObj)); // console: ['foo']</code></pre>
<p>如果你想获取一个对象的所有属性,，甚至包括不可枚举的，请查看<a href="Reference/Global_Objects/Object/getOwnPropertyNames" title="Object.getOwnPropertyNames()方法返回一个由指定对象的所有自身属性的属性名（包括不可枚举属性但不包括Symbol值作为名称的属性）组成的数组。"><code>Object.getOwnPropertyNames</code></a>。</p>
<h2 id="注意">注意</h2>
<p>在ES5里，如果此方法的参数不是对象（而是一个原始值），那么它会抛出 TypeError。在ES2015中，非对象的参数将被强制转换为一个对象。</p>
<pre><code  class="language-javascript">Object.keys("foo");
// TypeError: "foo" is not an object (ES5 code)

Object.keys("foo");
// ["0", "1", "2"]                   (ES2015 code)</code></pre>
<h2 id="Polyfill">Polyfill</h2>
<p>要在原生不支持的旧环境中添加兼容的<code>Object.keys</code>，请复制以下代码段：</p>
<pre><code  class="language-javascript">if (!Object.keys) {
  Object.keys = (function () {
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        hasDontEnumBug = !({toString: null}).propertyIsEnumerable('toString'),
        dontEnums = [
          'toString',
          'toLocaleString',
          'valueOf',
          'hasOwnProperty',
          'isPrototypeOf',
          'propertyIsEnumerable',
          'constructor'
        ],
        dontEnumsLength = dontEnums.length;

    return function (obj) {
      if (typeof obj !== 'object' &amp;&amp; typeof obj !== 'function' || obj === null) throw new TypeError('Object.keys called on non-object');

      var result = [];

      for (var prop in obj) {
        if (hasOwnProperty.call(obj, prop)) result.push(prop);
      }

      if (hasDontEnumBug) {
        for (var i=0; i &lt; dontEnumsLength; i++) {
          if (hasOwnProperty.call(obj, dontEnums[i])) result.push(dontEnums[i]);
        }
      }
      return result;
    }
  })()
};
</code></pre>
<p>上面的代码在IE7（也许IE8也是）下有个问题，就是如果传入一个来自其他 window 对象下的对象时，不可枚举的属性也会获取到。</p>
<p>另一个简单的实现，参见<a class="external" href="http://tokenposts.blogspot.com.au/2012/04/javascript-objectkeys-browser.html" rel="noopener">Javascript - Object.keys Browser Compatibility</a>。</p>
<h2 id="规范" style="margin-bottom: 20px; line-height: 30px;">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.14" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Object.keys</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.<br/>
    Implemented in JavaScript 1.8.5</td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-object.keys" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Object.keys</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-object.keys" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Object.keys</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容">浏览器兼容</h2>
<div>
<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>
<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>keys</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">
<span>Full support</span>
</abbr>
              5</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">
<span>Full support</span>
</abbr>
              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">
<span>Full support</span>
</abbr>
              4</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">
<span>Full support</span>
</abbr>
              9</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">
<span>Full support</span>
</abbr>
              12</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">
<span>Full support</span>
</abbr>
              5</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">
<span>Full support</span>
</abbr>
              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">
<span>Full support</span>
</abbr>
              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">
<span>Full support</span>
</abbr>
              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">
<span>Full support</span>
</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></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></dl></section></div><p></p>
</div>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Enumerability_and_ownership_of_properties">Enumerability and ownership of properties</a></li>
<li><a href="Reference/Global_Objects/Object/propertyIsEnumerable" title="propertyIsEnumerable() 方法返回一个布尔值，表示指定的属性是否可枚举。"><code>Object.prototype.propertyIsEnumerable()</code></a></li>
<li><a href="Reference/Global_Objects/Object/create" title="Object.create()方法创建一个新对象，使用现有的对象来提供新创建的对象的__proto__。 （请打开浏览器控制台以查看运行结果。）"><code>Object.create()</code></a></li>
<li><a href="Reference/Global_Objects/Object/getOwnPropertyNames" title="Object.getOwnPropertyNames()方法返回一个由指定对象的所有自身属性的属性名（包括不可枚举属性但不包括Symbol值作为名称的属性）组成的数组。"><code>Object.getOwnPropertyNames()</code></a></li>
<li><a href="Reference/Global_Objects/Object/values" title="Object.values()方法返回一个给定对象自身的所有可枚举属性值的数组，值的顺序与使用for...in循环的顺序相同 ( 区别在于 for-in 循环枚举原型链中的属性 )。"><code>Object.values()</code></a></li>
<li><a href="Reference/Global_Objects/Object/entries" 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.entries()</code></a></li>
</ul>
</article>