path: root/files/zh-cn/web/javascript/reference/statements/throw/index.html

---
title: throw
slug: Web/JavaScript/Reference/Statements/throw
tags:
  - JavaScript
  - Statement
translation_of: Web/JavaScript/Reference/Statements/throw
---
<div>{{jsSidebar("Statements")}}</div>

<p><strong><code>throw</code>语句</strong>用来抛出一个用户自定义的异常。当前函数的执行将被停止（<code>throw</code>之后的语句将不会执行），并且控制将被传递到调用堆栈中的第一个<a href="/zh-CN/docs/Web/JavaScript/Reference/Statements/try...catch"><code>catch</code></a>块。如果调用者函数中没有<code>catch</code>块，程序将会终止。</p>

<p>{{EmbedInteractiveExample("pages/js/statement-throw.html")}}</p>

<div class="hidden">
<p>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 href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>
</div>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">throw <em>expression</em>; </pre>

<dl>
 <dt><code>expression</code></dt>
 <dd>要抛出的表达式。</dd>
</dl>

<h2 id="描述">描述</h2>

<p>使用<code>throw</code>语句来抛出一个异常。当你抛出异常时，<code>expression</code> 指定了异常的内容。下面的每行都抛出了一个异常：</p>

<pre class="brush: js">throw "Error2"; // 抛出了一个值为字符串的异常
throw 42;       // 抛出了一个值为整数42的异常
throw true;     // 抛出了一个值为true的异常</pre>

<p>注意<code>throw</code>语句同样受到<a href="/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Automatic_semicolon_insertion">自动分号插入（ASI</a>）机制的控制，在<code>throw</code>关键字和值之间不允许有行终止符。</p>

<h2 id="示例">示例</h2>

<h3 id="抛出一个对象">抛出一个对象</h3>

<p>你可以在抛出异常时指定一个对象。然后可以在<code>catch</code>块中引用对象的属性。以下示例创建一个类型为<code>UserException</code>的对象，并在<code>throw</code>语句中使用它。</p>

<pre class="brush: js">function UserException(message) {
   this.message = message;
   this.name = "UserException";
}
function getMonthName(mo) {
   mo = mo-1; // 调整月份数字到数组索引 (1=Jan, 12=Dec)
   var months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul",
      "Aug", "Sep", "Oct", "Nov", "Dec"];
   if (months[mo] !== undefined) {
      return months[mo];
   } else {
      throw new UserException("InvalidMonthNo");
   }
}

try {
   // statements to try
   var myMonth = 15; // 15 超出边界并引发异常
   var monthName = getMonthName(myMonth);
} catch (e) {
   var monthName = "unknown";
   console.log(e.message, e.name); // 传递异常对象到错误处理
}
</pre>

<h3 id="另一个抛出异常对象的示例">另一个抛出异常对象的示例</h3>

<p>下面的示例中测试一个字符串是否是美国邮政编码。如果邮政编码是无效的，那么<code>throw</code>语句将会抛出一个类型为 <code>ZipCodeFormatException</code>的异常对象实例。</p>

<pre class="brush: js">/*
 * 创建 ZipCode 示例.
 *
 * 可被接受的邮政编码格式:
 *    12345
 *    12345-6789
 *    123456789
 *    12345 6789
 *
 * 如果构造函数参数传入的格式不符合以上任何一个格式，将会抛出异常。
 */

function ZipCode(zip) {
   zip = new String(zip);
   pattern = /[0-9]{5}([- ]?[0-9]{4})?/;
   if (pattern.test(zip)) {
      // zip code value will be the first match in the string
      this.value = zip.match(pattern)[0];
      this.valueOf = function() {
         return this.value
      };
      this.toString = function() {
         return String(this.value)
      };
   } else {
      throw new ZipCodeFormatException(zip);
   }
}

function ZipCodeFormatException(value) {
   this.value = value;
   this.message = "不是正确的邮政编码";
   this.toString = function() {
      return this.value + this.message
   };
}

/*
 * 这可能是一个验证美国地区中的脚本
 */

const ZIPCODE_INVALID = -1;
const ZIPCODE_UNKNOWN_ERROR = -2;

function verifyZipCode(z) {
   try {
      z = new ZipCode(z);
   } catch (e) {
      if (e instanceof ZipCodeFormatException) {
         return ZIPCODE_INVALID;
      } else {
         return ZIPCODE_UNKNOWN_ERROR;
      }
   }
   return z;
}

a = verifyZipCode(95060);         // 返回 95060
b = verifyZipCode(9560);          // 返回 -1
c = verifyZipCode("a");           // 返回 -1
d = verifyZipCode("95060");       // 返回 95060
e = verifyZipCode("95060 1234");  // 返回 95060 1234
</pre>

<h3 id="重新抛出异常">重新抛出异常</h3>

<p>你可以使用<code>throw</code>来抛出异常。下面的例子捕捉了一个异常值为数字的异常，并在其值大于50后重新抛出异常。重新抛出的异常传播到闭包函数或顶层，以便用户看到它。</p>

<pre class="brush: js">try {
   throw n; // 抛出一个数值异常
} catch (e) {
   if (e &lt;= 50) {
      // 异常在 1-50 之间时，直接处理
   } else {
      // 异常无法处理，重新抛出
      throw e;
   }
}
</pre>

<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>{{SpecName('ES3')}}</td>
   <td>{{Spec2('ES3')}}</td>
   <td>Initial definition. Implemented in JavaScript 1.4</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-12.13', 'throw statement')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-throw-statement', 'throw statement')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-throw-statement', 'throw statement')}}</td>
   <td>{{Spec2('ESDraft')}}</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 href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>

<p>{{Compat("javascript.statements.throw")}}</p>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/try...catch"><code>try...catch</code></a></li>
</ul>