A caught Typescript custom error cannot be checked for its type

Question

I created a custom typescript error, which based on several sources seems to go like this:

export class Exception extends Error {

    constructor(public message: string) {
        super(message);
        this.name = 'Exception';
        this.message = message;
        this.stack = (<any>new Error()).stack;
    }
    toString() {
        return this.name + ': ' + this.message;
    }
}

export class SpecificException extends Exception {

}

In my code I then throw this using a simple:

 throw new SpecificException('foo');

And elsewhere I catch it:

catch (e) {
  var t1 = Object.getPrototypeOf(e);
  var t2 = SpecificException.prototype;

  if (e instanceof SpecificException) {
    console.log("as expected");
  }
  else {
     console.log("not as expected");
  }
}

This code prints "not as expected". Any ideas why?

Later edit

As @basarat points out bellow, the error is of the expected type. Upon further investigation I realised that this was due to a module duplication having to do with my environment, possibly because of using mocha in watch mode.

Are you sure? For me both e instanceof Exception and e instanceof SpecificException are true. — Nitzan Tomer
– Nitzan Tomer, Commented Jun 14, 2016 at 21:39

basarat · Accepted Answer · 2016-06-15 00:26:27Z

5

Ran the following code:

declare global {
    interface Error {
        stack: any;
    } 
}
class Exception extends Error {

    constructor(public message: string) {
        super(message);
        this.name = 'Exception';
        this.message = message;
        this.stack = (<any>new Error()).stack;
    }
    toString() {
        return this.name + ': ' + this.message;
    }
}
class SpecificException extends Exception {

}

try {
  throw new SpecificException('foo');   
}
catch (e) {
  var t1 = Object.getPrototypeOf(e);
  var t2 = SpecificException.prototype;

  if (e instanceof SpecificException) {
    console.log("as expected");
  }
  else {
     console.log("not as expected");
  }
}

Got the desired outcome:

as expected

So there is no bug posted in the asked question 🌹

answered Jun 15, 2016 at 0:26

basarat

278k61 gold badges475 silver badges528 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

A caught Typescript custom error cannot be checked for its type

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related