yield

[rv] = yield [expression];

expression

. , undefined .

rv

, optional value next() .

yield yield [expression] caller . return .

yield value done IteratorResult . value yield (expression) , done (Boolean) .

yield , next() . next() :

• yield . next() , yield .
• throw . , .
• ; , IteratorResult caller undefined done true .
• return . , IteratorResult caller return done true .

optional value next() , optional value yield .

generator , yield, Generator.prototype.next() .

.

function* foo() {
  var index = 0;
  while (index <= 2)
    // when index reaches 3,
    // yield's done will be true
    // and its value will be undefined;
    yield index++;
}

, iterator .

var iterator = foo();
console.log(iterator.next()); // { value: 0, done: false }
console.log(iterator.next()); // { value: 1, done: false }
console.log(iterator.next()); // { value: 2, done: false }
console.log(iterator.next()); // { value: undefined, done: true }

See also

• The Iterator protocol
• function*
• function* expression
• yield*