files/zh-cn/web/javascript/reference/global_objects/string/repeat/index.html


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---
title: String.prototype.repeat()
slug: Web/JavaScript/Reference/Global_Objects/String/repeat
tags:
  - ECMAScript 2015
  - ES 6
  - JavaScript
  - Method
  - Prototype
  - Reference
  - String
  - polyfill
  - repeat()
  - 填充
translation_of: Web/JavaScript/Reference/Global_Objects/String/repeat
---
<p>{{JSRef}}</p>

<p><strong><code>repeat()</code></strong> 构造并返回一个新字符串，该字符串包含被连接在一起的指定数量的字符串的副本。</p>

<h2 id="Syntax" name="Syntax">语法</h2>

<pre class="syntaxbox notranslate"><code><var>str</var>.repeat(<var>count</var>)</code></pre>

<h3 id="Parameters" name="Parameters">参数</h3>

<dl>
 <dt><code>count</code></dt>
 <dd>介于 <code>0</code> 和 {{jsxref("Global_Objects/Number/POSITIVE_INFINITY", "+Infinity")}} 之间的整数。表示在新构造的字符串中重复了多少遍原字符串。</dd>
</dl>

<h3 id="返回值">返回值</h3>

<p> 包含指定字符串的指定数量副本的新字符串。</p>

<h3 id="Exceptions">Exceptions</h3>

<ul>
 <li>{{jsxref("Errors/Negative_repetition_count", "RangeError")}}: 重复次数不能为负数。</li>
 <li>{{jsxref("Errors/Resulting_string_too_large", "RangeError")}}: 重复次数必须小于 infinity，且长度不会大于最长的字符串。</li>
</ul>

<h2 id="兼容补丁Polyfill">兼容补丁(Polyfill)</h2>

<p>此方法已添加到 ECMAScript 2015 规范中，并且可能尚未在所有 JavaScript 实现中可用。然而，你可以使用以下代码段对 String.prototype.repeat() 进行填充：</p>

<pre class="brush: js  language-js notranslate"><code class="language-js"><span class="keyword token">if</span> <span class="punctuation token">(</span><span class="operator token">!</span>String<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>repeat<span class="punctuation token">)</span> <span class="punctuation token">{</span>
  String<span class="punctuation token">.</span>prototype<span class="punctuation token">.</span>repeat <span class="operator token">=</span> <span class="keyword token">function</span><span class="punctuation token">(</span>count<span class="punctuation token">)</span> <span class="punctuation token">{</span>
    <span class="string token">'use strict'</span><span class="punctuation token">;</span>
    <span class="keyword token">if</span> <span class="punctuation token">(</span><span class="keyword token">this</span> <span class="operator token">==</span> <span class="keyword token">null</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
      <span class="keyword token">throw</span> <span class="keyword token">new</span> <span class="class-name token">TypeError</span><span class="punctuation token">(</span><span class="string token">'can\'t convert '</span> <span class="operator token">+</span> <span class="keyword token">this</span> <span class="operator token">+</span> <span class="string token">' to object'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
    <span class="keyword token">var</span> str <span class="operator token">=</span> <span class="string token">''</span> <span class="operator token">+</span> <span class="keyword token">this</span><span class="punctuation token">;</span>
    count <span class="operator token">=</span> <span class="operator token">+</span>count<span class="punctuation token">;</span>
    <span class="keyword token">if</span> <span class="punctuation token">(</span>count <span class="operator token">!</span><span class="operator token">=</span> count<span class="punctuation token">)</span> <span class="punctuation token">{</span>
      count <span class="operator token">=</span> <span class="number token">0</span><span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
    <span class="keyword token">if</span> <span class="punctuation token">(</span>count <span class="operator token">&lt;</span> <span class="number token">0</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
      <span class="keyword token">throw</span> <span class="keyword token">new</span> <span class="class-name token">RangeError</span><span class="punctuation token">(</span><span class="string token">'repeat count must be non-negative'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
    <span class="keyword token">if</span> <span class="punctuation token">(</span>count <span class="operator token">==</span> <span class="number token">Infinity</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
      <span class="keyword token">throw</span> <span class="keyword token">new</span> <span class="class-name token">RangeError</span><span class="punctuation token">(</span><span class="string token">'repeat count must be less than infinity'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
    count <span class="operator token">=</span> Math<span class="punctuation token">.</span><span class="function token">floor<span class="punctuation token">(</span></span>count<span class="punctuation token">)</span><span class="punctuation token">;</span>
    <span class="keyword token">if</span> <span class="punctuation token">(</span>str<span class="punctuation token">.</span>length <span class="operator token">==</span> <span class="number token">0</span> <span class="operator token">||</span> count <span class="operator token">==</span> <span class="number token">0</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
      <span class="keyword token">return</span> <span class="string token">''</span><span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
   <span class="comment token"> // 确保 count 是一个 31 位的整数。这样我们就可以使用如下优化的算法。
    // 当前（2014年8月），绝大多数浏览器都不能支持 1 &lt;&lt; 28 长的字符串，所以：</span><span class="comment token">
</span>    <span class="keyword token">if</span> <span class="punctuation token">(</span>str<span class="punctuation token">.</span>length <span class="operator token">*</span> count <span class="operator token">&gt;=</span> <span class="number token">1</span> <span class="operator token">&lt;</span><span class="operator token">&lt;</span> <span class="number token">28</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
      <span class="keyword token">throw</span> <span class="keyword token">new</span> <span class="class-name token">RangeError</span><span class="punctuation token">(</span><span class="string token">'repeat count must not overflow maximum string size'</span><span class="punctuation token">)</span><span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
    <span class="keyword token">var</span> rpt <span class="operator token">=</span> <span class="string token">''</span><span class="punctuation token">;</span>
    <span class="keyword token">for</span> <span class="punctuation token">(</span><span class="punctuation token">;</span><span class="punctuation token">;</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
      <span class="keyword token">if</span> <span class="punctuation token">(</span><span class="punctuation token">(</span>count <span class="operator token">&amp;</span> <span class="number token">1</span><span class="punctuation token">)</span> <span class="operator token">==</span> <span class="number token">1</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
        rpt <span class="operator token">+</span><span class="operator token">=</span> str<span class="punctuation token">;</span>
      <span class="punctuation token">}</span>
      count <span class="operator token">&gt;</span><span class="operator token">&gt;</span><span class="operator token">&gt;=</span> <span class="number token">1</span><span class="punctuation token">;</span>
      <span class="keyword token">if</span> <span class="punctuation token">(</span>count <span class="operator token">==</span> <span class="number token">0</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
        <span class="keyword token">break</span><span class="punctuation token">;</span>
      <span class="punctuation token">}</span>
      str <span class="operator token">+</span><span class="operator token">=</span> str<span class="punctuation token">;</span>
    <span class="punctuation token">}</span>
    <span class="keyword token">return</span> rpt<span class="punctuation token">;</span>
  <span class="punctuation token">}</span>
<span class="punctuation token">}</span></code></pre>


<h2 id="Examples" name="Examples">示例</h2>

<pre class="brush:js notranslate"><span class="difflineplus">"abc".repeat(-1)     // </span>RangeError: repeat count must be positive and less than inifinity
<span class="difflineplus">"abc".repeat(0)      // ""</span>
<span class="difflineplus">"abc".repeat(1)      // "abc"</span>
<span class="difflineplus">"abc".repeat(2)      // "</span>abcabc<span class="difflineplus">"
</span>"abc".repeat(3.5)<span class="difflineplus">    // "abcabcabc" 参数count将会被自动转换成整数.
</span><span class="difflineplus">"abc".repeat(1/0)    //</span> RangeError: repeat count must be positive and less than inifinity

<span class="difflineplus">({toString : () =&gt; "abc", repeat : String.prototype.repeat}</span><span class="difflineplus">).repeat(2)
</span><span class="difflineplus">//"</span>abcabc<span class="difflineplus">",repeat是一个通用方法</span>,也就是它的调用者可以不是一个字符串对象.</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">规范</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-string.prototype.repeat', 'String.prototype.repeat')}}</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility" name="Browser_compatibility">浏览器兼容性</h2>

<p>{{Compat("javascript.builtins.String.repeat")}}</p>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{jsxref("String.prototype.concat()")}}</li>
</ul>