TypeScript 2.1.x fails to extend Error

[jamesadarich]

TypeScript Version: 2.1.4

Code

Given the following definition

export default class ExtendedError extends Error {
    public get something(): number {
        return 42;
    }

    public doSomething() {

    }

}

I get the following output for 2.0.3

const extendedErrorInstance = new ExtendedError();

console.log("Is instanceof ExtendedError:", extendedErrorInstance instanceof ExtendedError);
// outputs "Is instanceof ExtendedError: true"
console.log("Is instanceof Error:", extendedErrorInstance instanceof Error);
// outputs "Is instanceof Error: true"
console.log("Value of something:", extendedErrorInstance.something);
// outputs "Value of something: 42"
console.log("Do something:", extendedErrorInstance.doSomething());
// executes function and outputs "Do something: undefined"

However for version 2.1.1 and 2.1.4 I get the following

const extendedErrorInstance = new ExtendedError();

console.log("Is instanceof ExtendedError:", extendedErrorInstance instanceof ExtendedError);
// outputs "Is instanceof ExtendedError: false"
console.log("Is instanceof Error:", extendedErrorInstance instanceof Error);
// outputs "Is instanceof Error: true"
console.log("Value of something:", extendedErrorInstance.something);
// outputs "Value of something: undefined"
console.log("Do something:", extendedErrorInstance.doSomething());
// throws error "TypeError: extendedErrorInstance.doSomething is not a function"

Expected behavior:
The extended error to behave as in the first example

Actual behavior:
It seems as if the error has not been extended at all

Thanks very much for your assistance in advance.

James

[dbaeumer]

I got hit by the same problem.

[aluanhaddad]

This is an intended change.

[aluanhaddad]

This is documented here and very interesting, relevant discussions can be found in #12123 #12581 among others.

[dbaeumer]

@aluanhaddad thanks for the info. Would be cool to link this here as well: http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-1.html section Use returned values from super calls as ‘this’. I read this and having a pointer to the other doc would have saved quite some time.

[aluanhaddad]

@dbaeumer great point. That would definitely be good.

[andriijas]

I had this issue and I followed the recommendation in the linked related issues to remove extends Error. Seems to work.

[jamesadarich]

Ace, good to have the link because I missed too :)

@andriijas I've just made a small npm module to allow you to extend it adds a little easier and also so you don't have to set the prototype for errors that extend errors etc. (so handles the chaining for you) :)

https://www.npmjs.com/package/extendo-error

[aluanhaddad]

@jamesrichford +1 for initiative with the new package. -10 million for forking the web! 😆

[jamesadarich]

@aluanhaddad haha how do you mean breaking the web?

[aluanhaddad]

I meant to write "forking the web" but my brain isn't working at all today...

[blakeembrey]

@jamesrichford I would recommend using any of the existing packages on NPM today instead of making a new one. For instance, I use https://www.npmjs.com/package/make-error, but there's a few others.

One note on your code, I would do https://github.com/jamesrichford/extendo-error/blob/master/src/extendo-error.ts#L17 outside the constructor and not inside since it's really the same operation every time.

[jamesadarich]

@blakeembrey absolutely agree usually would but this package didn't come up on my searches thanks for pointing it out - will be useful for the future. Also thanks for the mini code review :)

[blakeembrey]

All good, finding quality modules on NPM can be tricky :) Especially for this, took me a while and various code reviews to decide I'd use and build with it going forward.