Generator.prototype.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

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 13 26 (26) No support (Yes) 10
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 5.1 (Yes) 26.0 (26) ? ? 10

See also

Document Tags and Contributors

 Contributors to this page: David_Gilbertson, Sebastianz, fscholz, redhead
 Last updated by: David_Gilbertson,