async function* expression

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

The async function* keywords can be used to define an async generator function inside an expression.

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

Try it

Syntax

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

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

Note: An expression statement cannot begin with the keywords async function to avoid ambiguity with an async function* declaration. The async function keywords only begin an expression when they appear 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

An async function* expression is very similar to, and has almost the same syntax as, an async function* declaration. The main difference between an async function* expression and an async function* declaration is the function name, which can be omitted in async function* expressions to create anonymous functions. An async 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 async iterable object. See also the chapter about functions for more information.

Examples

Using async function* expression

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

const x = async function* (y) {
  yield Promise.resolve(y * y);
};
x(6)
  .next()
  .then((res) => console.log(res.value)); // 36

Specifications

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

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
`async_function*`	63	79	55	50	12	63	55	46	12	8.0	63	1.0	10.0.0