uTools-Manuals/docs/javascript/Reference/Functions/Rest_parameters.html

<article id="wikiArticle">
<div></div>
<p><strong>剩余参数</strong>语法允许我们将一个不定数量的参数表示为一个数组。</p>
<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/functions-restparameters.html" width="100%"></iframe></div>
<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>
<h2 id="语法">语法</h2>
<pre><code  class="language-javascript">function(a, b, ...theArgs) {
  // ...
}
</code></pre>
<h2 id="描述">描述</h2>
<p>如果函数的最后一个命名参数以<code>...</code>为前缀，则它将成为一个由剩余参数组成的真数组，其中从<code>0</code>（包括）到<code>theArgs.length</code>（排除）的元素由传递给函数的实际参数提供。</p>
<p>在上面的例子中，<code>theArgs</code>将收集该函数的第三个参数（因为第一个参数被映射到<code>a</code>，而第二个参数映射到<code>b</code>）和所有后续参数。</p>
<h3 id="剩余参数和_arguments对象的区别">剩余参数和 <code>arguments</code>对象的区别</h3>
<p>剩余参数和 <code><a href="/zh-cn/JavaScript/Reference/Functions_and_function_scope/arguments" title="arguments">arguments</a></code>对象之间的区别主要有三个：</p>
<ul>
<li>剩余参数只包含那些没有对应形参的实参，而 <code>arguments</code> 对象包含了传给函数的所有实参。</li>
<li><code>arguments</code>对象不是一个真正的数组，而剩余参数是真正的 <code><a href="/zh-cn/JavaScript/Reference/Global_Objects/Array" title="Array">Array</a></code>实例，也就是说你能够在它上面直接使用所有的数组方法，比如 <code><a href="/zh-cn/JavaScript/Reference/Global_Objects/Array/sort" title="Array sort method">sort</a></code><font face="Open Sans, Arial, sans-serif">，</font><code><a href="/zh-cn/JavaScript/Reference/Global_Objects/Array/map" title="Array map method">map</a></code><font face="Open Sans, Arial, sans-serif">，</font><code><a href="/zh-cn/JavaScript/Reference/Global_Objects/Array/forEach" title="Array forEach method">forEach</a></code><font face="Open Sans, Arial, sans-serif">或</font><code><a href="/zh-cn/JavaScript/Reference/Global_Objects/Array/pop" title="Array pop method">pop</a></code>。</li>
<li><code>arguments</code>对象还有一些附加的属性 （如<code>callee</code>属性）。</li>
</ul>
<h3 id="从_arguments_到数组">从 arguments 到数组</h3>
<p>引入了剩余参数来减少由参数引起的样板代码。</p>
<pre><code>// Before rest parameters, "arguments" could be converted to a normal array using:

function f(a, b) {

  var normalArray = Array.prototype.slice.call(arguments);
  // -- or --
  var normalArray = [].slice.call(arguments);
  // -- or --
  var normalArray = Array.from(arguments);

  var first = normalArray.shift(); // OK, gives the first argument
  var first = arguments.shift(); // ERROR (arguments is not a normal array)

}

// Now we can easily gain access to a normal array using a rest parameter

function f(...args) {
  var normalArray = args;
  var first = normalArray.shift(); // OK, gives the first argument
}</code></code></pre>
<h3 id="解构剩余参数">解构剩余参数</h3>
<p>剩余参数可以被解构，这意味着他们的数据可以被解包到不同的变量中。请参阅<a href="Reference/Operators/Destructuring_assignment">解构赋值</a>。</p>
<pre><code  class="language-javascript">function f(...[a, b, c]) {
  return a + b + c;
}

f(1)          // NaN (b and c are undefined)
f(1, 2, 3)    // 6
f(1, 2, 3, 4) // 6 (the fourth parameter is not destructured)</code></pre>
<h2 id="Example" name="Example">示例</h2>
<p>因为<code>theArgs</code>是个数组，所以你可以使用<code>length</code>属性得到剩余参数的个数：</p>
<pre><code  class="language-javascript">function fun1(...theArgs) {
  alert(theArgs.length);
}
 
fun1();  // 弹出 "0", 因为theArgs没有元素
fun1(5); // 弹出 "1", 因为theArgs只有一个元素
fun1(5, 6, 7); // 弹出 "3", 因为theArgs有三个元素</code></pre>
<p>下例中，剩余参数包含了从第二个到最后的所有实参，然后用第一个实参依次乘以它们：</p>
<pre><code  class="language-javascript">function multiply(multiplier, ...theArgs) {
  return theArgs.map(function (element) {
    return multiplier * element;
  });
}

var arr = multiply(2, 1, 2, 3); 
console.log(arr);  // [2, 4, 6]
</code></pre>
<p>下例演示了你可以在剩余参数上使用任意的数组方法，而<code>arguments</code>对象不可以：</p>
<pre><code  class="language-javascript">function sortRestArgs(...theArgs) {
  var sortedArgs = theArgs.sort();
  return sortedArgs;
}
 
alert(sortRestArgs(5,3,7,1)); // 弹出 1,3,5,7
 
function sortArguments() {
  var sortedArgs = arguments.sort();
  return sortedArgs; // 不会执行到这里
}
 
alert(sortArguments(5,3,7,1)); // 抛出TypeError异常:arguments.sort is not a function
</code></pre>
<p>为了在<code>arguments</code>对象上使用<code>Array</code>方法，它必须首先被转换为一个真正的数组。</p>
<pre><code  class="language-javascript">function sortArguments() {
  var args = Array.prototype.slice.call(arguments);
  var sortedArgs = args.sort();
  return sortedArgs;
}
console.log(sortArguments(5, 3, 7, 1)); // shows 1, 3, 5, 7</code></pre>
<h2 id="Specifications" name="Specifications">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-262/6.0/#sec-function-definitions" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Function Definitions</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-function-definitions" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Function Definitions</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 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"><a href="Reference/Functions/rest_parameters">Rest parameters</a></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>
              47</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>
              15</td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</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>
              34</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>
              10</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>
              47</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>
              47</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>
              12</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>
              15</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>
              34</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>
              10</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>
              5.0</td><td class="bc-supports-yes bc-browser-nodejs bc-has-history"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              6.0.0<div class="bc-icons"></div><section class="bc-history" id="sect1"><dl><dt class="bc-supports-yes bc-supports"><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              6.0.0<div class="bc-icons"></div></dt><dd></dd><dt class="bc-supports-yes bc-supports"><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              4.0.0<div class="bc-icons"><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> </div></dt><dd><abbr class="only-icon" title="User must explicitly enable this feature."><span>Disabled</span><i class="ic-disabled"></i></abbr> From version 4.0.0: this feature is behind the <code>--harmony</code> runtime flag.</dd></dl></section></td></tr><tr><th scope="row">Destructuring rest parameters</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>
              49</td><td class="bc-supports-no bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</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>
              52</td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</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>
              36</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-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>
              49</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>
              49</td><td class="bc-supports-no bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</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>
              52</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>
              36</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-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>
              5.0</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="sect2"><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-no bc-supports">
<abbr class="bc-level bc-level-no only-icon" title="No support">
<span>No support</span>
                  
                </abbr></span></dt><dd>No 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><dt><abbr class="only-icon" title="User must explicitly enable this feature."><span>User must explicitly enable this feature.</span><i class="ic-disabled"></i></abbr></dt><dd>User must explicitly enable this feature.</dd></dl></section></div><p></p>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator" title="spread operator">Spread operator</a> (also ‘<code>...</code>’)</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/arguments" title="arguments">Arguments object</a></li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" title="Array">Array</a></li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions" title="Functions and function scope">Functions</a></li>
<li><a class="external" href="http://wiki.ecmascript.org/doku.php?id=harmony:rest_parameters" rel="noopener">Original proposal at ecmascript.org</a></li>
<li><a class="external" href="http://javascriptweblog.wordpress.com/2011/01/18/javascripts-arguments-object-and-beyond/" rel="noopener">JavaScript arguments object and beyond</a></li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">Destructuring assignment</a></li>
</ul>
</article>