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?
更新代码,将原型分配给Error。Prototype和instanceof以及你的断言工作。
function NotImplementedError(message = "") {
this.name = "NotImplementedError";
this.message = message;
}
NotImplementedError.prototype = Error.prototype;
不过,我会抛出你自己的对象并检查name属性。
throw {name : "NotImplementedError", message : "too lazy to implement"};
根据评论进行编辑
在看了评论并试图记住为什么我将prototype分配给Error后。而不是像Nicholas Zakas在他的文章中所做的new Error(),我用下面的代码创建了一个jsFiddle:
function NotImplementedError(message = "") {
this.name = "NotImplementedError";
this.message = message;
}
NotImplementedError.prototype = Error.prototype;
function NotImplementedError2(message = "") {
this.message = message;
}
NotImplementedError2.prototype = new Error();
try {
var e = new NotImplementedError("NotImplementedError message");
throw e;
} catch (ex1) {
console.log(ex1.stack);
console.log("ex1 instanceof NotImplementedError = " + (ex1 instanceof NotImplementedError));
console.log("ex1 instanceof Error = " + (ex1 instanceof Error));
console.log("ex1.name = " + ex1.name);
console.log("ex1.message = " + ex1.message);
}
try {
var e = new NotImplementedError2("NotImplementedError2 message");
throw e;
} catch (ex1) {
console.log(ex1.stack);
console.log("ex1 instanceof NotImplementedError2 = " + (ex1 instanceof NotImplementedError2));
console.log("ex1 instanceof Error = " + (ex1 instanceof Error));
console.log("ex1.name = " + ex1.name);
console.log("ex1.message = " + ex1.message);
}
控制台输出如下。
undefined
ex1 instanceof NotImplementedError = true
ex1 instanceof Error = true
ex1.name = NotImplementedError
ex1.message = NotImplementedError message
Error
at window.onload (http://fiddle.jshell.net/MwMEJ/show/:29:34)
ex1 instanceof NotImplementedError2 = true
ex1 instanceof Error = true
ex1.name = Error
ex1.message = NotImplementedError2 message
这证实了我遇到的“问题”是错误的堆栈属性是创建new error()的行号,而不是抛出e发生的地方。然而,这可能比NotImplementedError.prototype.name = "NotImplementedError"行影响Error对象的副作用要好。
另外,注意NotImplementedError2,当我没有显式地设置.name时,它等于“Error”。然而,正如评论中提到的,因为该版本将prototype设置为new Error(),所以我可以设置NotImplementedError2.prototype.name = "NotImplementedError2"并OK。
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');
}
如果你使用Node/Chrome。下面的代码片段将为您提供满足以下要求的扩展。
err instanceof Error
err instanceof CustomErrorType
console.log() returns [CustomErrorType] when created with a message
console.log() returns [CustomErrorType: message] when created without a message
throw/stack provides the information at the point the error was created.
Works optimally in Node.JS, and Chrome.
Will pass instanceof checks in Chrome, Safari, Firefox and IE 8+, but will not have a valid stack outside of Chrome/Safari. I'm OK with that because I can debug in chrome, but code which requires specific error types will still function cross browser. If you need Node only you can easily remove the if statements and you're good to go.
片段
var CustomErrorType = function(message) {
if (Object.defineProperty) {
Object.defineProperty(this, "message", {
value : message || "",
enumerable : false
});
} else {
this.message = message;
}
if (Error.captureStackTrace) {
Error.captureStackTrace(this, CustomErrorType);
}
}
CustomErrorType.prototype = new Error();
CustomErrorType.prototype.name = "CustomErrorType";
使用
var err = new CustomErrorType("foo");
输出
var err = new CustomErrorType("foo");
console.log(err);
console.log(err.stack);
[CustomErrorType: foo]
CustomErrorType: foo
at Object.<anonymous> (/errorTest.js:27:12)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3
/errorTest.js:30
throw err;
^
CustomErrorType: foo
at Object.<anonymous> (/errorTest.js:27:12)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3