References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript await statement

Statement JavaScript All modern browsers Updated
Quick answer

The await keyword pauses an async function until a promise settles, then resumes with its resolved value. const data = await response.json(). It only works inside an async function (or a module's top level) and turns promise-based code into clean, sequential-looking lines.

Overview

await unwraps a promise. Put it before a promise-returning call and the async function pauses there until the promise resolves, then continues with the resolved value as if it had been there all along. That's what lets you write const user = await getUser() instead of getUser().then(user => ...) — the asynchronous result reads like a normal variable.

It comes with one firm rule: await only works inside an async function (or at the top level of an ES module). Use it in a plain function and you get a syntax error. So await and async always travel together — the async marks the function, the await does the pausing.

If the awaited promise rejects, the await throws, which you catch with a normal try...catch. One performance note: awaiting promises one after another runs them sequentially. When the operations don't depend on each other, start them together and await with Promise.all([...]) so they run in parallel — a frequent and easy speed-up.

Syntax

async function getData() {
  const res = await fetch("/api");   // pause until it resolves
  const data = await res.json();
  return data;
}

// parallel, not sequential
const [a, b] = await Promise.all([fetchA(), fetchB()]);

Example

Live example 
<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  const delay = (val, ms) => new Promise(r => setTimeout(() => r(val), ms));

  async function run() {
    const out = document.getElementById('out');
    out.textContent = 'Working...';

    const a = await delay('first', 400);
    const b = await delay('second', 400);

    out.textContent = 'Got: ' + a + ', ' + b;
  }

  run();
</script>

Best practices

  • Use await only inside an async function (or a module's top level).
  • Wrap awaited calls in try...catch to handle rejected promises.
  • Run independent awaits in parallel with await Promise.all([...]), not one after another.
  • Don't await inside forEach() — use a for...of loop for sequential awaiting.

Frequently asked questions

What does await do in JavaScript?
It pauses the surrounding async function until the promise settles, then resumes with the resolved value.
Where can I use await?
Inside an async function, or at the top level of an ES module. Using it in a regular function is a syntax error.
How do I handle an error from await?
Wrap it in try...catch — a rejected promise throws at the await.
How do I await multiple promises at once?
Use await Promise.all([p1, p2]) to run them in parallel and wait for all to finish.
async function break