I dont think that this is an appropriate implementation. Cause is usually an optional parameter.

new FastifyError(new Error('casue')) syntax doesn't looks good to me. I think it's better to follow actual JavaScript implmentation:

new FastifyError('message', {
  casue: new Error('casue')
})

i'm also okay with this idea, using named arguments

new FastifyError({
  message: 'message',
  casue: new Error('casue')
})

Also hasCause option for createError function is not really needed.
I believe it can be dynamic

Also hasCause option for createError function is not really needed. I believe it can be dynamic

I am thinking how to make this backward compatible since the function FastifyError accepts a rest arg, maybe it will be needed to change the interface of the function accepting an object instead of positional parameters. Any idea?

@DanieleFedeli I have no idea, but i think it's okay to release a major version if needed

I am thinking how to make this backward compatible since the function FastifyError accepts a rest arg, maybe it will be needed to change the interface of the function accepting an object instead of positional parameters. Any idea?

It doesn't really matter for the ...rest.

function Error(...args) {
  if(args.length && typeof args.at(-1) === 'object' && 'cause' in args.at(-1)) {
    this.cause = args.pop()
  }
}

Should I fix for node 14?

Yes, please.

@Uzlopak could you do a final check?

@mcollina :)