Web/JavaScript/Reference/Global objects/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 are always 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.

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
ECMAScript (ECMA-262)The definition of 'GeneratorFunction' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`GeneratorFunction`	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