Web/JavaScript/Reference/Operators/await

The await operator is used to wait for a Promise. It can only be used inside an async function.

Syntax

[rv] = await expression;

expression: A Promise or any value to wait for.
rv: Returns the fulfilled value of the promise, or the value itself if it's not a Promise.

Description

The await expression causes async function execution to pause until a Promise is settled (that is, fulfilled or rejected), and to resume execution of the async function after fulfillment. When resumed, the value of the await expression is that of the fulfilled Promise.

If the Promise is rejected, the await expression throws the rejected value.

If the value of the expression following the await operator is not a Promise, it's converted to a resolved Promise.

An await splits execution flow, allowing the caller of the async function to resume execution. After the await defers the continuation of the async function, execution of subsequent statements ensues. If this await is the last expression executed by its function execution continues by returning to the function's caller a pending Promise for completion of the await's function and resuming execution of that caller.

Examples

Awaiting a promise to be fulfilled

If a Promise is passed to an await expression, it waits for the Promise to be fulfilled and returns the fulfilled value.

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

async function f1() {
  var x = await resolveAfter2Seconds(10);
  console.log(x); // 10
}

f1();

Thenable objects

Thenable objects will be fulfilled just the same.

async function f2() {
  const thenable = {
    then: function(resolve, _reject) {
      resolve('resolved!')
    }
  };
  console.log(await thenable); // resolved!
}

f2();

Conversion to promise

If the value is not a Promise, it converts the value to a resolved Promise, and waits for it.

async function f3() {
  var y = await 20;
  console.log(y); // 20
}

f3();

Promise rejection

If the Promise is rejected, the rejected value is thrown.

async function f4() {
  try {
    var z = await Promise.reject(30);
  } catch(e) {
    console.error(e); // 30
  }
}

f4();

Handling rejected promises

Handle rejected Promise without try block.

var response = await promisedFunction().catch((err) => { console.error(err); });
// response will be undefined if the promise is rejected

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'async functions' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`await`	Chrome Full support 55	Edge Full support 14	Firefox Full support 52	IE No support No	Opera Full support 42	Safari Full support 10.1	WebView Android Full support 55	Chrome Android Full support 55	Firefox Android Full support 52	Opera Android Full support 42	Safari iOS Full support 10.3	Samsung Internet Android Full support 6.0	nodejs 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.