generator.next

The next() method returns an object with two properties done and value. You can also provide a parameter to the next method to send a value to the generator.

Syntax

gen.next(value)

Parameters

value

The value to send to the generator.

Return value

An Object with two properties:

• done (boolean)
  • Has the value true if the iterator is past the end of the iterated sequence. In this case value optionally specifies the return value of the iterator.
  • Has the value false if the iterator was able to produce the next value in the sequence. This is equivalent of not specifying the done property altogether.
• value - any JavaScript value returned by the iterator. Can be omitted when done is true.

Examples

Using next()

The following example shows a simple generator and the object that the next method returns:

function* gen() { 
  yield 1;
  yield 2;
  yield 3;
}

var g = gen(); // "Generator { }"
g.next();      // "Object { value: 1, done: false }"
g.next();      // "Object { value: 2, done: false }"
g.next();      // "Object { value: 3, done: false }"
g.next();      // "Object { value: undefined, done: true }"

Sending values to the generator

In this example, next is called with a value. Note that the first call did not log anything, because the generator was not yielding anything initially.

function* gen() {
  while(true) {
    var value = yield null;
    console.log(value);
  }
}

var g = gen();
g.next(1); 
// "{ value: null, done: false }"
g.next(2); 
// "{ value: null, done: false }"
// 2

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Generator.prototype.next' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'Generator.prototype.next' in that specification.	Draft

Browser compatibility

See also

• function*
• Iterators and generators