AsyncFunction

The AsyncFunction 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 could be obtained by evaluating the following code.

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

Syntax

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

Parameters

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".

functionBody

A string containing the JavaScript statements comprising the function definition.

Description

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.

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

Properties

AsyncFunction.length

The AsyncFunction constructor's length property whose value is 1.

AsyncFunction.prototype

Allows the addition of properties to all async function objects.

AsyncFunction prototype object

Properties

AsyncFunction.constructor

The initial value is AsyncFunction.

AsyncFunction.prototype[@@toStringTag]

Returns "AsyncFunction".

AsyncFunction instances

AsyncFunction instances inherit methods and properties from AsyncFunction.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all AsyncFunction instances.

Examples

Creating an async function from an AsyncFunction constructor

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

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

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

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

Specifications

Browser compatibility

See also

• async function function
• async function expression
• Function
• function statement
• function expression
• Functions and function scope