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

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。

其他回答

更简单的方法。你可以让你的对象从Error对象继承。 例子:

function NotImplementError(message)
{
    this.message = message;
    Error.call();
    Error.call(message);
} 

我们所做的是使用函数call()调用Error类的构造函数,因此基本上与在其他面向对象语言中实现类继承是一样的。

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:

尝试为用户定义的错误类型的每个实例创建一个新的原型对象。它允许instanceof检查像往常一样运行,并且在Firefox和V8 (Chome, nodejs)中正确报告类型和消息。

function NotImplementedError(message){
    if(NotImplementedError.innercall===undefined){
        NotImplementedError.innercall = true;
        NotImplementedError.prototype = new Error(message);
        NotImplementedError.prototype.name = "NotImplementedError";
        NotImplementedError.prototype.constructor = NotImplementedError;

        return new NotImplementedError(message);
    }
    delete NotImplementedError.innercall;
}

注意,一个额外的条目将在正确的堆栈之前。

这是最快的方法:

    let thisVar = false

    if (thisVar === false) {
            throw new Error("thisVar is false. It should be true.")
    }

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