jsschools

await

Pauses an async function until a promise settles and yields its resolved value.

Since ES2017 Spec ↗

Syntax

const value = await promise;

Returns

any — The fulfillment value of the awaited promise; throws if it rejects.

Throws

  • any — The awaited promise rejects, propagating the rejection reason.

Examples

function delay(ms, v) {
  return new Promise(r => setTimeout(() => r(v), ms));
}
async function main() {
  const x = await delay(0, 7);
  console.log(x);
}
main();
Output 
7

async function run() {
  try {
    await Promise.reject(new Error("nope"));
  } catch (e) {
    console.log(e.message);
  }
}
run();
Output 
nope

async function values() {
  const [a, b] = await Promise.all([
    Promise.resolve(1),
    Promise.resolve(2),
  ]);
  console.log(a + b);
}
values();
Output 
3

Notes

- `await` is valid inside async functions and at module top level. - Awaiting a non-promise wraps it and resolves immediately. - Wrap awaited calls in `try...catch` to handle rejections.

Browser & runtime support

EnvironmentSince version
chrome 55
firefox 52
safari 11
edge 15
node 7.6

See also