The async function* keywords can be used to define an asynchronous generator function inside an expression.
You can also define async generator functions using the async function* declaration.
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 functionto avoid ambiguity with anasync function*declaration. Theasync functionkeywords only begin an expression when they appear in a context that cannot accept statements.
Parameters
name- : The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.
paramN- : The name of a formal parameter for the function. For the parameters' syntax, see the Functions reference.
statements- : 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*
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