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  • `super` and superclass constructor return values

`super` and superclass constructor return values

# Isiah Meadows (9 years ago)

What should this be in class B? The value of object or an instance of B? It's an edge case, but could simplify my code a little if it's the former.

const object = {}

class A {
  constructor() {
    return object
  }
}

class B extends A {
  constructor() {
    super()
    console.log(this === object)
  }
}
# Eric Faust (9 years ago)

My understanding is that this should log "true". Class constructors may return any object they wish, and needn't return instances of the class.

Hopefully, this will allow you to simplify.

Thanks,

# Logan Smyth (9 years ago)

Yup, correct. The value of the this binding is initialized to the result of [[Construct]], which will either be the parent constructor this binding, or the explicitly returned value.

Relevant spec links: Evaluating super(): (12.3.5.1) www.ecma-international.org/ecma-262/6.0/#sec-super-keyword-runtime-semantics-evaluation Returning a value from a constructor: (9.2.2 step 13.b) www.ecma-international.org/ecma-262/6.0/#sec