The AsyncFunction constructor creates a new async function object. In JavaScript, every asynchronous function is actually an AsyncFunction object.

Note that AsyncFunction is not a global object. It can be obtained with the following code:

Object.getPrototypeOf(async function(){}).constructor


new AsyncFunction([arg1[, arg2[, ...argN]],] functionBody)


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".
A string containing the JavaScript statements comprising the function definition.


async function objects created with the AsyncFunction constructor are parsed when the function is created. This is less efficient than declaring an async function with an async 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: async functions created with the AsyncFunction 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 AsyncFunction constructor was called.

This is different from using eval with code for an async function expression.

Invoking the AsyncFunction constructor as a function (without using the new operator) has the same effect as invoking it as a constructor.


Creating an async function from an AsyncFunction() constructor

function resolveAfter2Seconds(x) {
  return new Promise(resolve => {
    setTimeout(() => {
    }, 2000);

let AsyncFunction = Object.getPrototypeOf(async function(){}).constructor

let a = new AsyncFunction('a',
                          'return await resolveAfter2Seconds(a) + await resolveAfter2Seconds(b);');

a(10, 20).then(v => {
  console.log(v); // prints 30 after 4 seconds


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

Browser compatibility

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
AsyncFunctionChrome Full support 55Edge Full support 15Firefox Full support 52IE No support NoOpera Full support 42Safari Full support 10.1WebView Android Full support 55Chrome Android Full support 55Firefox Android Full support 52Opera Android Full support 42Safari iOS Full support 10.3Samsung Internet Android Full support 6.0nodejs Full support 7.6.0
Full support 7.6.0
Full support 7.0.0
Disabled From version 7.0.0: this feature is behind the --harmony runtime flag.


Full support
Full support
No support
No support
User must explicitly enable this feature.
User must explicitly enable this feature.

See also