instanceof doesn't work for extended builtin types

[hbakhtiyor]

TypeScript Version: 1.8.7

Code

export class CustomError extends Error {
    name = "CustomError";

    constructor() {
        super();
        this.message = "message";
    }
}
const err = new CustomError();
console.log(err instanceof CustomError); // => false

[vknez]

I have the same issue with TypeScript 2.1.1.

[vknez]

Apparently, there are other issues referencing the same, i.e. #12279, #12123, #12058.

[DanielRosenwasser]

I'm marking this as a duplicate of #12123. This is an intentional breaking change and documented here. Sorry about the inconveniences due to this change.