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.
- The value will be assigned as a result of a
yield
expression. For example, invariable = yield expression
, the value passed to the.next()
function will be assigned tovariable
.
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 casevalue
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 thedone
property altogether. value
- Any JavaScript value returned by the iterator. Can be omitted when
done
istrue
.
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; } const 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 }"
Using next() with a list
function* getPage(pageSize = 1, list) { let output = []; let index = 0; while (index < list.length) { output = []; for (let i = index; i < index + pageSize; i++) { if (list[i]) { output.push(list[i]); } } yield output; index += pageSize; } } list = [1, 2, 3, 4, 5, 6, 7, 8] var page = getPage(3, list); // Generator { } page.next(); // Object {value: (3) [1, 2, 3], done: false} page.next(); // Object {value: (3) [4, 5, 6], done: false} page.next(); // Object {value: (2) [7, 8], done: false} page.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 does not log anything, because the generator was not yielding anything initially.
function* gen() { while (true) { let value = yield null; console.log(value); } } const g = gen(); g.next(1); // "{ value: null, done: false }" g.next(2); // 2 // "{ value: null, done: false }"
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Generator.prototype.next' in that specification. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
next | Chrome Full support 39 | Edge Full support 13 | Firefox Full support 26 | IE No support No | Opera Full support 26 | Safari Full support 10 | WebView Android Full support 39 | Chrome Android Full support 39 | Firefox Android Full support 26 | Opera Android Full support 26 | Safari iOS Full support 10 | Samsung Internet Android Full support 4.0 | nodejs Full support Yes |
Legend
- Full support
- Full support
- No support
- No support