uTools-Manuals/docs/javascript/Reference/Global_Objects/String/substring.html

<article id="wikiArticle">
<p></p><p></p>
<p><strong><code>substring() </code></strong>方法返回一个字符串在开始索引到结束索引之间的一个子集, 或从开始索引直到字符串的末尾的一个子集。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code><var>str</var>.substring(<var>indexStart</var>[, <var>indexEnd</var>])</code></code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code>indexStart</code></dt>
<dd>需要截取的第一个字符的索引，该字符作为返回的字符串的首字母。</dd>
<dt><code>indexEnd</code></dt>
<dd>可选。一个 0 到字符串长度之间的整数，以该数字为索引的字符不包含在截取的字符串内。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>包含给定字符串的指定部分的新字符串。</p>
<h2 id="Description" name="Description">描述</h2>
<p><code>substring</code> 提取从 <code>indexStart</code> 到 <code>indexEnd</code>（不包括）之间的字符。特别地：</p>
<ul>
<li>如果 <code>indexStart</code> 等于 <code>indexEnd</code>，<code>substring</code> 返回一个空字符串。</li>
<li>如果省略 <code>indexEnd</code>，<code>substring</code> 提取字符一直到字符串末尾。</li>
<li>如果任一参数小于 0 或为 <a href="Reference/Global_Objects/NaN" title="全局属性 NaN 的值表示不是一个数字（Not-A-Number）。"><code>NaN</code></a>，则被当作 0。</li>
<li>如果任一参数大于 <code>stringName.length</code>，则被当作 <code>stringName.length</code>。</li>
<li>如果 <code>indexStart</code> 大于 <code>indexEnd</code>，则 <code>substring</code> 的执行效果就像两个参数调换了一样。见下面的例子。</li>
</ul>
<h2 id="Examples" name="Examples">示例</h2>
<h3 id="Example:_Using_substring" name="Example:_Using_substring">例子：使用 <code>substring</code></h3>
<p>下例使用 <code>substring</code> 输出字符串 "<code>Mozilla</code>" 中的字符：</p>
<pre><code class="language-js">var anyString = "Mozilla";

// 输出 "Moz"
console.log(anyString.substring(0,3));
console.log(anyString.substring(3,0));
console.log(anyString.substring(3,-3));
console.log(anyString.substring(3,NaN));
console.log(anyString.substring(-2,3));
console.log(anyString.substring(NaN,3));

// 输出 "lla"
console.log(anyString.substring(4,7));
console.log(anyString.substring(7,4));

// 输出 ""
console.log(anyString.substring(4,4));

// 输出 "Mozill"
console.log(anyString.substring(0,6));

// 输出 "Mozilla"
console.log(anyString.substring(0,7));
console.log(anyString.substring(0,10));
</code></pre>
<p> </p>
<h3 id="运用_length_属性来使用_substring()"><strong>运用 length 属性来使用 substring()</strong></h3>
<p>下面一个例子运用了    String.length 属性去获取指定字符串的倒数元素。显然这个办法更容易记住，因为你不再像上面那个例子那样去记住起始位置和最终位置。</p>
<pre><code  class="language-javascript"><code>// Displays 'illa' the last 4 characters
var anyString = 'Mozilla';
var anyString4 = anyString.substring(anyString.length - 4);
console.log(anyString4);</code>

// Displays 'zilla' the last 5 characters
var anyString = 'Mozilla';
var anyString5 = anyString.substring(anyString.length - 5);
console.log(anyString5);</code></pre>
<p> </p>
<h3 id="Example:_Replacing_a_substring_within_a_string" name="Example:_Replacing_a_substring_within_a_string">例子：替换一个字符串的子字符串</h3>
<p>下例替换了一个字符串中的子字符串。可以替换单个字符和子字符串。该例结尾调用的函数将 "<code>Brave New World</code>" 变成了 "<code>Brave New Web</code>"。</p>
<pre><code class="language-js">function replaceString(oldS, newS, fullS) {
// Replaces oldS with newS in the string fullS
  for (var i = 0; i &lt; fullS.length; i++) {
    if (fullS.substring(i, i + oldS.length) == oldS) {
     fullS = fullS.substring(0, i) + newS + fullS.substring(i + oldS.length, fullS.length);
    }
  }
  return fullS;
}

replaceString("World", "Web", "Brave New World");</code></pre>
<p>需要注意的是，如果 <code>oldS</code> 是 <code>newS</code> 的子字符串将会导致死循环。例如，尝试把 "World" 替换成 "OtherWorld"。一个更好的方法如下：</p>
<pre><code class="language-js">function replaceString(oldS, newS,fullS){
  return fullS.split(oldS).join(newS);
}</code></pre>
<p><span style="line-height: 1.5;">上面的代码只是子字符串操作的一个例子。如果你需要替换子字符串，更多时候会用到 </span><span style="line-height: 1.5em;"><a href="Reference/Global_Objects/String/replace" title="replace() 方法返回一个由替换值（replacement）替换一些或所有匹配的模式（pattern）后的新字符串。模式可以是一个字符串或者一个正则表达式，替换值可以是一个字符串或者一个每次匹配都要调用的回调函数。"><code>String.prototype.replace()</code></a>。</span></p>
<h2 id="规范">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>ECMAScript 1st Edition.</td>
<td>Standard</td>
<td>Implemented in JavaScript 1.0</td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.5.4.15" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">String.prototype.substring</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-string.prototype.substring" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">String.prototype.substring</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div><p></p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
</tr>
</tbody>
</table>
</div>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li><a href="Reference/Global_Objects/String/substr" title="substr() 方法返回一个字符串中从指定位置开始到指定字符数的字符。"><code>String.prototype.substr()</code></a></li>
<li><a href="Reference/Global_Objects/String/slice" title="slice() 方法提取一个字符串的一部分，并返回一新的字符串。"><code>String.prototype.slice()</code></a></li>
</ul>
</article>