I'm trying to find a reference somewhere in the spec that defines this behaviour but I haven't managed to find one. With regenerator the following will throw an error of Generator has already finished:

function* generator(){
  yield 5;
}
var iterator = generator();
console.log(iterator.next());
console.log(iterator.next());
console.log(iterator.next());

While v8 will run it just fine.

{ value: 5, done: false }
{ value: undefined, done: true }
{ value: undefined, done: true }

Is regenerator or v8 the one in the wrong here?