我可以在JavaScript中为用户定义的异常定义自定义类型吗?如果是,我该怎么做?
当前回答
你应该创建一个扩展Error的自定义异常:
class InvalidArgumentException extends Error {
constructor(message) {
super(message);
this.name = this.constructor.name;
}
}
注意:设置this.name是. tostring()和.stack打印InvalidArgumentException而不是Error所必需的。
对于旧的Javascript环境,你可以做原型继承:
function InvalidArgumentException(message) {
this.message = message;
// Use V8's native method if available, otherwise fallback
if ("captureStackTrace" in Error)
Error.captureStackTrace(this, InvalidArgumentException);
else
this.stack = (new Error()).stack;
}
InvalidArgumentException.prototype = Object.create(Error.prototype);
InvalidArgumentException.prototype.name = "InvalidArgumentException";
InvalidArgumentException.prototype.constructor = InvalidArgumentException;
这基本上是一个简化版本的disfated与增强堆栈跟踪工作在Firefox和其他浏览器。
两者都满足所有这些测试:
用法:
throw new InvalidArgumentException();
var err = new InvalidArgumentException("Not yet...");
它的行为是预期的:
err instanceof InvalidArgumentException // -> true
err instanceof Error // -> true
InvalidArgumentException.prototype.isPrototypeOf(err) // -> true
Error.prototype.isPrototypeOf(err) // -> true
err.constructor.name // -> InvalidArgumentException
err.name // -> InvalidArgumentException
err.message // -> Not yet...
err.toString() // -> InvalidArgumentException: Not yet...
err.stack // -> works fine!
其他回答
你可以实现你自己的异常和它们的处理,例如:
// define exceptions "classes"
function NotNumberException() {}
function NotPositiveNumberException() {}
// try some code
try {
// some function/code that can throw
if (isNaN(value))
throw new NotNumberException();
else
if (value < 0)
throw new NotPositiveNumberException();
}
catch (e) {
if (e instanceof NotNumberException) {
alert("not a number");
}
else
if (e instanceof NotPositiveNumberException) {
alert("not a positive number");
}
}
还有另一种捕获类型化异常的语法,尽管这并不适用于所有浏览器(例如不是在IE中):
// define exceptions "classes"
function NotNumberException() {}
function NotPositiveNumberException() {}
// try some code
try {
// some function/code that can throw
if (isNaN(value))
throw new NotNumberException();
else
if (value < 0)
throw new NotPositiveNumberException();
}
catch (e if e instanceof NotNumberException) {
alert("not a number");
}
catch (e if e instanceof NotPositiveNumberException) {
alert("not a positive number");
}
//create error object
var error = new Object();
error.reason="some reason!";
//business function
function exception(){
try{
throw error;
}catch(err){
err.reason;
}
}
现在我们设置,添加原因或任何我们想要的属性到错误对象并检索它。通过使误差更合理。
请参见MDN中的示例。
如果你需要定义多个error(在这里测试代码!):
function createErrorType(name, initFunction) {
function E(message) {
this.message = message;
if (Error.captureStackTrace)
Error.captureStackTrace(this, this.constructor);
else
this.stack = (new Error()).stack;
initFunction && initFunction.apply(this, arguments);
}
E.prototype = Object.create(Error.prototype);
E.prototype.name = name;
E.prototype.constructor = E;
return E;
}
var InvalidStateError = createErrorType(
'InvalidStateError',
function (invalidState, acceptedStates) {
this.message = 'The state ' + invalidState + ' is invalid. Expected ' + acceptedStates + '.';
});
var error = new InvalidStateError('foo', 'bar or baz');
function assert(condition) { if (!condition) throw new Error(); }
assert(error.message);
assert(error instanceof InvalidStateError);
assert(error instanceof Error);
assert(error.name == 'InvalidStateError');
assert(error.stack);
error.message;
在JavaScript中,什么是扩展错误的好方法?
我经常使用带有原型继承的方法。重写toString()的好处是,像Firebug这样的工具将记录实际信息,而不是将[object object]记录到控制台,以查找未捕获的异常。
使用instanceof来确定异常的类型。
main.js
// just an exemplary namespace
var ns = ns || {};
// include JavaScript of the following
// source files here (e.g. by concatenation)
var someId = 42;
throw new ns.DuplicateIdException('Another item with ID ' +
someId + ' has been created');
// Firebug console:
// uncaught exception: [Duplicate ID] Another item with ID 42 has been created
Exception.js
ns.Exception = function() {
}
/**
* Form a string of relevant information.
*
* When providing this method, tools like Firebug show the returned
* string instead of [object Object] for uncaught exceptions.
*
* @return {String} information about the exception
*/
ns.Exception.prototype.toString = function() {
var name = this.name || 'unknown';
var message = this.message || 'no description';
return '[' + name + '] ' + message;
};
DuplicateIdException.js
ns.DuplicateIdException = function(message) {
this.name = 'Duplicate ID';
this.message = message;
};
ns.DuplicateIdException.prototype = new ns.Exception();
ES6
使用新的类和扩展关键字,现在更容易:
class CustomError extends Error {
constructor(message) {
super(message);
//something
}
}