JavaScript Async/Await Cheat Sheet

Covers async function syntax, error handling with try/catch, and running promises sequentially versus concurrently with Promise combinators.

1 PageIntermediateApr 8, 2026

Basic async/await

async functions always return a Promise.

javascript

async function fetchUser(id) {  const response = await fetch(`/api/users/${id}`);  const data = await response.json();  return data;}// An async function always returns a PromisefetchUser(1).then(user => console.log(user));// Equivalent, inside another async functionasync function main() {  const user = await fetchUser(1);  console.log(user);}

Error Handling

Wrap awaited calls in try/catch/finally.

javascript

async function loadUser(id) {  try {    const res = await fetch(`/api/users/${id}`);    if (!res.ok) {      throw new Error(`HTTP ${res.status}`);    }    return await res.json();  } catch (err) {    console.error("Failed to load user:", err.message);    return null;  } finally {    console.log("request finished");  }}

Sequential vs Parallel

Awaiting in sequence pays the latency cost multiple times.

javascript

// Sequential -- each await blocks the next (slower, ~2x time)async function sequential() {  const a = await fetchUser(1);  const b = await fetchUser(2);  return [a, b];}// Parallel -- both requests start immediatelyasync function parallel() {  const [a, b] = await Promise.all([fetchUser(1), fetchUser(2)]);  return [a, b];}// Parallel, tolerant of individual failuresasync function parallelSettled() {  const results = await Promise.allSettled([fetchUser(1), fetchUser(2)]);  return results.filter(r => r.status === "fulfilled").map(r => r.value);}

Iteration & Top-Level Await

Looping with await and module-level await.

javascript

async function processAll(ids) {  const results = [];  for (const id of ids) {    results.push(await fetchUser(id));   // Runs one at a time  }  return results;}// Top-level await (in ES modules only)const config = await fetch("/config.json").then(r => r.json());

Promise Combinators

Ways to combine multiple promises.

Promise.all()- Waits for all promises; rejects immediately if any one rejects
Promise.allSettled()- Waits for all promises; never short-circuits, returns a status per item
Promise.race()- Resolves/rejects as soon as the first promise settles
Promise.any()- Resolves with the first fulfilled promise; rejects only if all reject
await- Pauses the async function until the promise settles, unwrapping its value
async function- Always returns a Promise, even if the body has no explicit await

Pro Tip

Awaiting independent promises one-by-one inside a loop serializes requests unnecessarily — start them all first (e.g. with map + Promise.all) so they run concurrently instead of paying the latency cost N times.

Was this cheat sheet helpful?

JavaScript DOM Manipulation Cheat Sheet

JavaScript Closures Cheat Sheet

Explore Topics

#JavaScriptAsyncAwait#JavaScriptAsyncAwaitCheatSheet#Programming#Intermediate#BasicAsyncAwait#ErrorHandling#SequentialVsParallel#Iteration#Functions#Concurrency#CheatSheet#SkillVeris

Sri Hayavadhana Info-Tech

Professional Web Designing Services