How Error class could be extended in TypeScript

Question

Is there a way to extend Error in TypeScript >= 3.3 so it would correctly work with instanceof?

class MyError extends Error {
  constructor(
                    message: string,
    public readonly details: string
  ) { super(message) }
}

try {
  throw new MyError('some message', 'some details')
} catch (e) {
  console.log(e.message)            // Ok
  console.log(e.details)            // Ok
  console.log(e instanceof MyError) // Wrong, prints false
}

Take a look at this: https://stackoverflow.com/questions/31626231/custom-error-class-in-typescript — moronator, Mar 11 '19 at 19:31

score 1 · Answer 1 · answered Mar 11 '19 at 19:37

1

Thanks to @moronator, you have to add magic line

class MyError extends Error {
  constructor(
                    message: string,
    public readonly details: string
  ) { 
    super(message) 

    // This line
    Object.setPrototypeOf(this, MyError.prototype)
  }
}

try {
  throw new MyError('some message', 'some details')
} catch (e) {
  console.log(e.message)            // Ok
  console.log(e.details)            // Ok
  console.log(e instanceof MyError) // Works
}

answered Mar 11 '19 at 19:37

Alex Craft

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Where did you find this? – Nino Filiu Mar 11 '19 at 19:44
related: https://stackoverflow.com/questions/52402166/property-setprototypeof-does-not-exist-on-type-objectconstructor – Nino Filiu Mar 11 '19 at 19:49
See first comment answered by @moronator, there's the link to the answer – Alex Craft Mar 12 '19 at 20:23

How Error class could be extended in TypeScript

1 Answers1