Discussion on: Central Error Handling in Express

[Thinh Nguyen]

Great Article, Thanks

btw, I got a small question in this own Error class :

class ErrorHandler extends Error {
  constructor(statusCode, message) {
    super();
    this.statusCode = statusCode;
    this.message = message;
  }
}
module.exports = {
  ErrorHandler
}

Why we have to write like this (1)

super();
this.message = message;

but not like this (2)

super(message);

?

Actually, I wrote like (2) and then my own class lost a message property

It only comes back when I change it to (1).

What is the difference between them ?

Thanks,

[Chinedu Orie]

The super() method is used when a class (child) inherits from another class (parent).
The super() method provides a means of syncing the child's constructor to the parent's constructor.
Let me illustrate with an example

class Foor {
    constructor(name) {
        this.name = name
   }
    printName = () => {
      console.log(this.name);
   }
}

class Bar extends Foo {

     constructor(name) {
         super(name)
   }
}

const bar = new Bar('Test');

bar.printName() // Test


Now, looking at the code above,Foorequires anameto be passed to its constructor in order to function, whenBarinherited fromFoo, there's no way thenamecould be passed down toFooif not with thesuper()`

So, in relation to the snippet that you shared above, you are passing the message to the parent which in this case is Error, that way the child ErrorHandler has no access to message

I hope this helps.

[Alexey Vorobyov]

Is there a necessity in Bar constructor at all?
You just pass the same Test value to the parent class ultimately. In this case
there is no need to a constructor at all I assume and Eslint should also hint about it.