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");
}
其他回答
使用throw语句。
JavaScript并不关心异常类型(就像Java一样)。 JavaScript只是注意到,有一个异常,当你捕捉到它,你可以“看看”异常“说”什么。
如果你有不同的异常类型,你必须抛出,我建议使用变量包含异常的字符串/对象,即消息。在需要它的地方使用“throw myException”,在catch中,将捕获的异常与myException进行比较。
从WebReference:
throw {
name: "System Error",
level: "Show Stopper",
message: "Error detected. Please contact the system administrator.",
htmlMessage: "Error detected. Please contact the <a href=\"mailto:sysadmin@acme-widgets.com\">system administrator</a>.",
toString: function(){return this.name + ": " + this.message;}
};
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();
//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。
function MyError(message) {
this.message = message;
}
MyError.prototype = new Error;
这允许使用像..
try {
something();
} catch(e) {
if(e instanceof MyError)
doSomethingElse();
else if(e instanceof Error)
andNowForSomethingCompletelyDifferent();
}