Nasi wolontariusze nie przetłumaczyli jeszcze tego artykułu na język Polski. Dołącz do nas i pomóż go przetłumaczyć!
Można także przeczytać artykuł w języku: English (US).

The async function keyword can be used to define async functions inside expressions.

You can also define async functions using an async function statement.

Syntax

async function [name]([param1[, param2[, ..., paramN]]]) {
   statements
}

As of ES2015, you can also use arrow functions.

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 an argument to be passed to the function.
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 statement. The main difference between an async function expression and an async function statement 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. See also the chapter about functions for more information.

Examples

Simple example

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


var add = async function(x) { // async function expression assigned to a variable
  var a = await resolveAfter2Seconds(20);
  var b = await resolveAfter2Seconds(30);
  return x + a + b;
};

add(10).then(v => {
  console.log(v);  // prints 60 after 4 seconds.
});


(async function(x) { // async function expression used as an IIFE
  var p_a = resolveAfter2Seconds(20);
  var p_b = resolveAfter2Seconds(30);
  return x + await p_a + await p_b;
})(10).then(v => {
  console.log(v);  // prints 60 after 2 seconds.
});

Specifications

Specification Status Comment
ECMAScript Latest Draft (ECMA-262)
The definition of 'async function' in that specification.
Draft  
ECMAScript 2018 (ECMA-262)
The definition of 'async function' in that specification.
Standard  
ECMAScript 2017 (ECMA-262)
The definition of 'async function' in that specification.
Standard Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Basic supportChrome 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 55Edge Mobile Full support 15Firefox Android Full support 52Opera Android Full support 42Safari iOS Full support 10.1Samsung Internet Android Full support 6.0nodejs Full support 7.6.0
Full support 7.6.0
Full support 7.0.0
Disabled
Disabled From version 7.0.0: this feature is behind the --harmony runtime flag.

Legend

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

See also

Autorzy i etykiety dokumentu

Ostatnia aktualizacja: ExE-Boss,