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The Generator
object is returned by a generator function and it conforms to both the iterable protocol and the iterator protocol.
Syntax
function* gen() { yield 1; yield 2; yield 3; } var g = gen(); // "Generator { }"
Methods
Generator.prototype.next()
- Returns a value yielded by the
yield
expression. Generator.prototype.return()
- Returns the given value and finishes the generator.
Generator.prototype.throw()
- Throws an error to a generator.
Example
An infinite iterator
function* idMaker(){ var index = 0; while(true) yield index++; } var gen = idMaker(); // "Generator { }" console.log(gen.next().value); // 0 console.log(gen.next().value); // 1 console.log(gen.next().value); // 2 // ...
Legacy generator objects
Firefox (SpiderMonkey) also implements an earlier version of generators in JavaScript 1.7, where the star (*) in the function declaration was not necessary (you just use the yield
keyword in the function body). However, legacy generators are deprecated. Do not use them; they are going to be removed (bug 1083482).
Legacy generator methods
Generator.prototype.next()
- Returns a value yielded by the
yield
expression. This corresponds tonext()
in the ES6 generator object. Generator.prototype.close()
- Closes the generator, so that when calling
next()
anStopIteration
error will be thrown. This corresponds to thereturn()
method in the ES6 generator object. Generator.prototype.send()
- Used to send a value to a generator. The value is returned from the
yield
expression, and returns a value yielded by the nextyield
expression.send(x)
corresponds tonext(x)
in the ES6 generator object. Generator.
prototype.
throw()
- Throws an error to a generator. This corresponds to the
throw()
method in the ES6 generator object.
Legacy generator example
function* fibonacci() { var a = yield 1; yield a * 2; } var it = fibonacci(); console.log(it); // "Generator { }" console.log(it.next()); // 1 console.log(it.send(10)); // 20 console.log(it.close()); // undefined console.log(it.next()); // throws StopIteration (as the generator is now closed)
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Generator objects' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Generator objects' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 39.0 | (Yes) | No support | No support | No support |
Feature | Android | Android Webview | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|
Basic support | No support | 39.0 | (Yes) | No support | No support | No support | 39.0 |
See also
Legacy generators
- The legacy generator function
- The legacy generator function expression
StopIteration
- The legacy Iterator protocol
ES6 generators
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