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。
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 https://github.com/mdn/interactive-examples and send us a pull request.
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"; // 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
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; // 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 }
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。
/* * 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
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; // 抛出一个数值异常 } catch (e) { if (e <= 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; } }
规范
Specification | Status | Comment |
---|---|---|
ECMAScript 3rd Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.4 |
ECMAScript 5.1 (ECMA-262) throw statement |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) throw statement |
Standard | |
ECMAScript Latest Draft (ECMA-262) throw statement |
Draft |
浏览器兼容
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out
https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
throw |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support