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.

Try it

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*

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

Specification
ECMAScript Language Specification
# sec-generator-function-definitions

Browser compatibility

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See also