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function* expression

The function* keyword can be used to define a generator function inside an expression.

You can also define generator functions using the function* declaration.

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Syntax

js
function* (param0) {
  statements
}
function* (param0, param1) {
  statements
}
function* (param0, param1, /* …, */ paramN) {
  statements
}

function* name(param0) {
  statements
}
function* name(param0, param1) {
  statements
}
function* name(param0, param1, /* …, */ paramN) {
  statements
}

Note: An expression statement cannot begin with the keyword function to avoid ambiguity with a function* declaration. The function keyword only begins an expression when it appears in a context that cannot accept statements.

Parameters

name Optional

The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.

paramN Optional

The name of a formal parameter for the function. For the parameters' syntax, see the Functions reference.

statements Optional

The statements which comprise the body of the function.

Description

A function* expression is very similar to, and has almost the same syntax as, a function* declaration. The main difference between a function* expression and a function* declaration is the function name, which can be omitted in function* expressions to create anonymous functions. A function* expression can be used as an IIFE (Immediately Invoked Function Expression) which runs as soon as it is defined, allowing you to create an ad-hoc iterable iterator object. See also the chapter about functions for more information.

Examples

Using function* expression

The following example defines an unnamed generator function and assigns it to x. The function yields the square of its argument:

js
const x = function* (y) {
  yield y * y;
};

Specifications

Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Opera Safari Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet WebView Android Deno Node.js
function* 49 12 26 36 10 49 26 36 10 5.0 49 1.0 4.0.0
trailing_comma 58 79 52 45 10 58 52 43 10 7.0 58 1.0 8.0.0

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/function*