Contextual this in prototype functions

[pankleks]

Hi,

When adding new functions to object prototype, this could be hard-typed in below scenario:

interface Array<T> {
  first(): T;
}

Array.prototype.first = function() {
  return this.length > 0 ? this[0] : undefined;
}

this is of type any, why it can't be of type Array ?

typescript: 1.8.30

[RyanCavanaugh]

Duplicate of #8024 ?