非常教程

JavaScript参考手册

声明 | Statements

throw

throw语句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(throw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catch块。如果调用者函数中没有catch块,程序将会终止。

语法

throw expression; 

expression要抛出的表达式。

描述

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

throw 'Error2'; // generates an exception with a string value
throw 42;       // generates an exception with the value 42
throw true;     // generates an exception with the value true

注意throw语句同样受到自动分号插入(ASI)机制的控制,在throw关键字和值之间不允许有行终止符。

示例

抛出一个对象

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

function UserException(message) {
   this.message = message;
   this.name = 'UserException';
}
function getMonthName(mo) {
   mo = mo - 1; // Adjust month number for array index (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 is out of bound to raise the exception
   var monthName = getMonthName(myMonth);
} catch (e) {
   monthName = 'unknown';
   console.log(e.message, e.name); // pass exception object to err handler
}

另一个抛出异常对象的示例

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throw语句将会抛出一个类型为ZipCodeFormatException的异常对象实例。

/*
 * Creates a ZipCode object.
 *
 * Accepted formats for a zip code are:
 *    12345
 *    12345-6789
 *    123456789
 *    12345 6789
 *
 * If the argument passed to the ZipCode constructor does not
 * conform to one of these patterns, an exception is thrown.
 */

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 = 'does not conform to the expected format for a zip code';
   this.toString = function() {
      return this.value + this.message;
   };
}

/*
 * This could be in a script that validates address data
 * for US addresses.
 */

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);         // returns 95060
b = verifyZipCode(9560);          // returns -1
c = verifyZipCode('a');           // returns -1
d = verifyZipCode('95060');       // returns 95060
e = verifyZipCode('95060 1234');  // returns 95060 1234

重新抛出异常

你可以使用throw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。

try {
   throw n; // throws an exception with a numeric value
} catch (e) {
   if (e <= 50) {
      // statements to handle exceptions 1-50
   } else {
      // cannot handle this exception, so rethrow
      throw e;
   }
}

规范

Specification

Status

Comment

ECMAScript 3rd Edition (ECMA-262)

Standard

Initial definition. Implemented in JavaScript 1.4

ECMAScript 5.1 (ECMA-262)The definition of 'throw statement' in that specification.

Standard

ECMAScript 2015 (6th Edition, ECMA-262)The definition of 'throw statement' in that specification.

Standard

ECMAScript Latest Draft (ECMA-262)The definition of 'throw statement' in that specification.

Living Standard

浏览器兼容性

Feature

Chrome

Edge

Firefox (Gecko)

Internet Explorer

Opera

Safari

Basic support

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

Feature

Android

Chrome for Android

Edge

Firefox Mobile (Gecko)

IE Mobile

Opera Mobile

Safari Mobile

Basic support

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

JavaScript

JavaScript 是一种高级编程语言,通过解释执行,是一门动态类型,面向对象(基于原型)的解释型语言。它已经由ECMA(欧洲电脑制造商协会)通过 ECMAScript 实现语言的标准化。它被世界上的绝大多数网站所使用,也被世界主流浏览器( Chrome、IE、FireFox、Safari、Opera )支持。JavaScript 是一门基于原型、函数先行的语言,是一门多范式的语言,它支持面向对象编程,命令式编程,以及函数式编程。它提供语法来操控文本、数组、日期以及正则表达式等,不支持 I/O,比如网络