如何在JavaScript中创建自定义错误？ [英] How do I create a custom Error in JavaScript?

问题描述

由于某种原因，构造函数委派在以下代码段中不起作用：

 函数NotImplementedError（）{
 Error.apply（this，arguments）; 
} 
 NotImplementedError.prototype = new Error（）; 
 
 var nie = new NotImplementedError（some message）; 
 console.log（消息是：+ nie.message +'）
  

运行它给出消息是：''。任何想法为什么，或者如果有更好的方法来创建一个新的错误子类？ c $ c> c c c

解决方案

更新您的代码，将您的原型分配给Error.prototype，instanceof和您的断言工作。

 函数NotImplementedError（message）{
 this.name =NotImplementedError; 
 this.message =（message ||）; 
} 
 NotImplementedError.prototype = Error.prototype; 
  

但是，我只是抛出自己的对象，只需检查name属性。

  throw {name：NotImplementedError，message：too lazy to implement}; 
  

根据评论进行修改

查看评论后，试图记住为什么我会将原型分配给 Error.prototype 而不是 new Error（）像Nicholas Zakas在他的文章，我创建了一个 jsFiddle ，其代码如下： p>

  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）;}  

控制台输出是这样的。

  undefined 
 ex1 instanceof NotImplementedError = true 
 ex1 instanceof错误= true 
 ex1.name = NotImplementedError 
 ex1.message = NotImplementedError消息
错误
在window.onload（http://fiddle.jshell.net/MwMEJ/show/ ：29：34）
 ex1 instanceof NotImplementedError2 = true 
 ex1 instanceof Error = true 
 ex1.name =错误
 ex1.message = NotImplementedError2消息
  

这证实了我遇到的问题是错误的堆栈属性是行号，其中新错误（）被创建，而不是发生 throw e 的位置。但是，对于影响Error对象的 NotImplementedError.prototype.name =NotImplementedError行的副作用可能会更好。

另外，当我没有明确地设置 .name 时，请注意 NotImplementedError2 等于错误。但是，如注释所述，由于该版本将原型设置为 new Error（），我可以设置 NotImplementedError2.prototype.name =NotImplementedError2 并且OK。

For some reason it looks like constructor delegation doesn't work in the following snippet:

function NotImplementedError() { 
  Error.apply(this, arguments); 
}
NotImplementedError.prototype = new Error();

var nie = new NotImplementedError("some message");
console.log("The message is: '"+nie.message+"'")

Running this gives The message is: ''. Any ideas as to why, or if there is a better way to create a new Error subclass? Is there a problem with applying to the native Error constructor that I don't know about?

解决方案

Update your code to assign your prototype to the Error.prototype and the instanceof and your asserts work.

function NotImplementedError(message) {
    this.name = "NotImplementedError";
    this.message = (message || "");
}
NotImplementedError.prototype = Error.prototype;

However, I would just throw your own object and just check the name property.

throw {name : "NotImplementedError", message : "too lazy to implement"}; 

Edit based on comments

After looking at the comments and trying to remember why I would assign prototype to Error.prototype instead of new Error() like Nicholas Zakas did in his article, I created a jsFiddle with the code below:

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);
}

The console output was this.

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

This confirmes the "problem" I ran into was the stack property of the error was the line number where new Error() was created, and not where the throw e occurred. However, that may be better that having the side effect of a NotImplementedError.prototype.name = "NotImplementedError" line affecting the Error object.

Also, notice with NotImplementedError2, when I don't set the .name explicitly, it is equal to "Error". However, as mentioned in the comments, because that version sets prototype to new Error(), I could set NotImplementedError2.prototype.name = "NotImplementedError2" and be OK.

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