出于某种原因，在下面的代码段中，构造函数委托似乎不起作用:
function NotImplementedError() {
Error.apply(this, arguments);
}
NotImplementedError.prototype = new Error();
var nie = new NotImplementedError("some message");
console.log("The message is: '"+nie.message+"'")
运行该命令得到的消息是:"。有什么想法，为什么，或者是否有更好的方法来创建一个新的错误子类?是否有一个问题，应用到本机错误构造函数，我不知道?
当前回答
我使用构造函数模式来创建新的错误对象。我定义了原型链，比如Error实例。请参阅MDN错误构造函数参考。
你可以查看这段关于要点的片段。
实现
// Creates user-defined exceptions
var CustomError = (function() {
'use strict';
//constructor
function CustomError() {
//enforces 'new' instance
if (!(this instanceof CustomError)) {
return new CustomError(arguments);
}
var error,
//handles the arguments object when is passed by enforcing a 'new' instance
args = Array.apply(null, typeof arguments[0] === 'object' ? arguments[0] : arguments),
message = args.shift() || 'An exception has occurred';
//builds the message with multiple arguments
if (~message.indexOf('}')) {
args.forEach(function(arg, i) {
message = message.replace(RegExp('\\{' + i + '}', 'g'), arg);
});
}
//gets the exception stack
error = new Error(message);
//access to CustomError.prototype.name
error.name = this.name;
//set the properties of the instance
//in order to resemble an Error instance
Object.defineProperties(this, {
stack: {
enumerable: false,
get: function() { return error.stack; }
},
message: {
enumerable: false,
value: message
}
});
}
// Creates the prototype and prevents the direct reference to Error.prototype;
// Not used new Error() here because an exception would be raised here,
// but we need to raise the exception when CustomError instance is created.
CustomError.prototype = Object.create(Error.prototype, {
//fixes the link to the constructor (ES5)
constructor: setDescriptor(CustomError),
name: setDescriptor('JSU Error')
});
function setDescriptor(value) {
return {
configurable: false,
enumerable: false,
writable: false,
value: value
};
}
//returns the constructor
return CustomError;
}());
使用
CustomError构造函数可以接收许多参数来构建消息，例如:
var err1 = new CustomError("The url of file is required"),
err2 = new CustomError("Invalid Date: {0}", +"date"),
err3 = new CustomError("The length must be greater than {0}", 4),
err4 = new CustomError("Properties .{0} and .{1} don't exist", "p1", "p2");
throw err4;
这是自定义错误的样子:
其他回答
我也遇到过类似的问题。我的错误需要是error和NotImplemented的实例，它还需要在控制台中产生一致的回溯。
我的解决方案:
var NotImplemented = (function() {
var NotImplemented, err;
NotImplemented = (function() {
function NotImplemented(message) {
var err;
err = new Error(message);
err.name = "NotImplemented";
this.message = err.message;
if (err.stack) this.stack = err.stack;
}
return NotImplemented;
})();
err = new Error();
err.name = "NotImplemented";
NotImplemented.prototype = err;
return NotImplemented;
}).call(this);
// TEST:
console.log("instanceof Error: " + (new NotImplemented() instanceof Error));
console.log("instanceof NotImplemented: " + (new NotImplemented() instanceofNotImplemented));
console.log("message: "+(new NotImplemented('I was too busy').message));
throw new NotImplemented("just didn't feel like it");
使用node.js运行的结果:
instanceof Error: true
instanceof NotImplemented: true
message: I was too busy
/private/tmp/t.js:24
throw new NotImplemented("just didn't feel like it");
^
NotImplemented: just didn't feel like it
at Error.NotImplemented (/Users/colin/projects/gems/jax/t.js:6:13)
at Object.<anonymous> (/Users/colin/projects/gems/jax/t.js:24:7)
at Module._compile (module.js:449:26)
at Object.Module._extensions..js (module.js:467:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.runMain (module.js:487:10)
at process.startup.processNextTick.process._tickCallback (node.js:244:9)
该错误通过了我的所有3个标准，尽管stack属性是非标准的，但在大多数较新的浏览器中都支持它，这在我的情况下是可以接受的。
我喜欢这样做:
利用name，使toString()抛出"{code}: {message}" 将相同的东西返回给super，这样在stacktrace中就会显示相同的内容 将代码附加到错误。在代码中检查/解析代码比检查消息(例如，您可能希望本地化消息)更好 将消息附加到错误。message作为error.toString()的替代
class AppException extends Error { constructor(code, message) { const fullMsg = message ? `${code}: ${message}` : code; super(fullMsg); this.name = code; this.code = code; this.message = fullMsg; } toString() { return this.message; } } // Just a code try { throw new AppException('FORBIDDEN'); } catch(e) { console.error(e); console.error(e.toString()); console.log(e.code === 'FORBIDDEN'); } // A code and a message try { throw new AppException('FORBIDDEN', 'You don\'t have access to this page'); } catch(e) { console.error(e); console.error(e.toString()); console.log(e.code === 'FORBIDDEN'); }
我使用构造函数模式来创建新的错误对象。我定义了原型链，比如Error实例。请参阅MDN错误构造函数参考。
你可以查看这段关于要点的片段。
实现
// Creates user-defined exceptions
var CustomError = (function() {
'use strict';
//constructor
function CustomError() {
//enforces 'new' instance
if (!(this instanceof CustomError)) {
return new CustomError(arguments);
}
var error,
//handles the arguments object when is passed by enforcing a 'new' instance
args = Array.apply(null, typeof arguments[0] === 'object' ? arguments[0] : arguments),
message = args.shift() || 'An exception has occurred';
//builds the message with multiple arguments
if (~message.indexOf('}')) {
args.forEach(function(arg, i) {
message = message.replace(RegExp('\\{' + i + '}', 'g'), arg);
});
}
//gets the exception stack
error = new Error(message);
//access to CustomError.prototype.name
error.name = this.name;
//set the properties of the instance
//in order to resemble an Error instance
Object.defineProperties(this, {
stack: {
enumerable: false,
get: function() { return error.stack; }
},
message: {
enumerable: false,
value: message
}
});
}
// Creates the prototype and prevents the direct reference to Error.prototype;
// Not used new Error() here because an exception would be raised here,
// but we need to raise the exception when CustomError instance is created.
CustomError.prototype = Object.create(Error.prototype, {
//fixes the link to the constructor (ES5)
constructor: setDescriptor(CustomError),
name: setDescriptor('JSU Error')
});
function setDescriptor(value) {
return {
configurable: false,
enumerable: false,
writable: false,
value: value
};
}
//returns the constructor
return CustomError;
}());
使用
CustomError构造函数可以接收许多参数来构建消息，例如:
var err1 = new CustomError("The url of file is required"),
err2 = new CustomError("Invalid Date: {0}", +"date"),
err3 = new CustomError("The length must be greater than {0}", 4),
err4 = new CustomError("Properties .{0} and .{1} don't exist", "p1", "p2");
throw err4;
这是自定义错误的样子:
上面的很多方法都不起作用。
最后一个是一个实际的错误。如果您使用字符串，它看起来很好，但它不会提供堆栈跟踪。如果你抛出错误，你不能有“Uncaught BadError: bad”，所以你必须删除自定义错误(遗憾的是)。如果你抛出一个对象，它看起来有点偏离，最后一个只是一个平均错误。
此方法创建一个具有自定义名称的错误，同时保留堆栈跟踪:
var errProto = Object.create(Error.prototype, { constructor: { value: Error, enumerable: false, writable: true, configurable: true } }) var isFirefox = !!window.InstallTrigger // Hide stack for Firefox only, as stacks can cause problems with high "frame" counts. function createError(name, message, hideStack) { if (message == null) { message = "" } var customError = Error(message) customError.name = name Object.setPrototypeOf(customError, errProto) if (isFirefox && hideStack) { customError.stack = "" } else if (isFirefox) { var stack = customError.stack var newline = stack.indexOf("\n") + 1 stack = stack.slice(newline) customError.stack = stack var split = stack.split(":") if (split.length > 4) { var a = split[3] var b = split[4] var t = b.slice(0, b.indexOf("\n")) customError.lineNumber = Number(a) customError.columnNumber = Number(t) } } else { var stack = customError.stack var split = stack.split("\n") var secondPart = split.slice(2).join("\n") stack = split[0] + "\n" + secondPart customError.stack = stack var split = secondPart.split(":") var a = split[2] var b = split[3] } throw customError } var frame = 0 function aFunction() { if (++frame === 100) { createError("LazyError", "function getting lazy", false, true) } else { requestAnimationFrame(aFunction) } } setTimeout(aFunction, Math.random() * 500) * { font-family: Verdana; } Check your inspector!
以不能使用instanceof为代价，下面的代码保留了原始的堆栈跟踪，并且没有使用任何非标准的技巧。
// the function itself
var fixError = function(err, name) {
err.name = name;
return err;
}
// using the function
try {
throw fixError(new Error('custom error message'), 'CustomError');
} catch (e) {
if (e.name == 'CustomError')
console.log('Wee! Custom Error! Msg:', e.message);
else
throw e; // unhandled. let it propagate upwards the call stack
}
