Inherit from Error breaks `instanceof` check in TypeScript

inheritance, instanceof, types, typescript

Solution

Turns out an change has been introduced in TypeScript@2.1 that breaks this pattern. The whole breaking change is described here.

In general it seems it's too complicated/error to even go with this direction.

Probably better to have own error object and keeps some original `Error` as an property:

class CustomError {
    originalError: Error;

    constructor(originalError?: Error) {
        if (originalError) {
            this.originalError = originalError
        }
    }
}

class SpecificError extends CustomError {}

const error = new SpecificError(new Error('test'));

console.log(error instanceof CustomError); // true
console.log(error instanceof SpecificError); // true

Problem

Can someone explain me why the `error instanceof CustomError` part of below code is `false` ? ``` class CustomError extends Error {} const error = new CustomError(); console.log(error instanceof Error); // true console.log(error instanceof CustomError); // false ??? class ParentClass {} class ChildClass extends ParentClass { } const child = new ChildClass(); console.log(child instanceof ParentClass); // true console.log(child instanceof ChildClass); // true ``` Is something special about Error object? I would like to make my own error types that i can check against. Btw i've checked the above code on latest TypeScript Playground

Original source