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GeneratorFunction

The GeneratorFunction constructor creates a new generator function object. In JavaScript every generator function is actually a GeneratorFunction object.

Note that GeneratorFunction is not a global object. It could be obtained by evaluating the following code.

Object.getPrototypeOf(function*(){}).constructor

Syntax

new GeneratorFunction ([arg1[, arg2[, ...argN]],] functionBody)

Parameters

arg1, arg2, ... argN
Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example "x", "theValue", or "a,b".
functionBody
A string containing the JavaScript statements comprising the function definition.

Description

generator function objects created with the GeneratorFunction constructor are parsed when the function is created. This is less efficient than declaring a generator function with a function* expression and calling it within your code, because such functions are parsed with the rest of the code.

All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed.

Note: generator function created with the GeneratorFunction constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the GeneratorFunction constructor was called. This is different from using eval with code for a generator function expression.

Invoking the GeneratorFunction constructor as a function (without using the new operator) has the same effect as invoking it as a constructor.

Properties

GeneratorFunction.length
The GeneratorFunction constructor's length property whose value is 1.
GeneratorFunction.prototype
Allows the addition of properties to all generator function objects.

GeneratorFunction prototype object

Properties

GeneratorFunction.constructor
The initial value is GeneratorFunction.
GeneratorFunction.prototype.prototype
The value is %GeneratorPrototype%.

GeneratorFunction instances

GeneratorFunction instances inherit methods and properties from GeneratorFunction.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all GeneratorFunction instances.

Examples

Creating a generator function from a GeneratorFunction constructor

var GeneratorFunction = Object.getPrototypeOf(function*(){}).constructor
var g = new GeneratorFunction("a", "yield a * 2");
var iterator = g(10);
console.log(iterator.next().value); // 20

Specifications

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

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 26 (26) ? ? ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? (Yes) 26 (26) ? ? ?

See also

Document Tags and Contributors

 Contributors to this page: fscholz, SphinxKnight, arai
 Last updated by: fscholz,