Promises vs async/await in JavaScript

Same foundation

async/await is syntactic sugar over Promises. An async function always returns a Promise. await pauses the async function's execution until that Promise settles, without blocking the JavaScript thread from running other tasks.

Syntax and readability

Promise chains shine for short pipelines. async/await shines when you have branching, loops, or try/catch around several steps. Prefer the style that makes control flow obvious to the next reader — including interviewers reading your screen share.

Error propagation

Rejected promises skip to the next .catch. await throws into the surrounding try/catch of an async function. Forgetting to await a rejecting promise is a common bug: the function continues and the rejection becomes unhandled. Always await (or explicitly void with a catch) every Promise that can fail.

Sequential vs parallel

// sequential — each waits
const a = await fetchA();
const b = await fetchB();

// parallel — start together
const [a, b] = await Promise.all([fetchA(), fetchB()]);

Interviewers listen for whether you accidentally serialize independent I/O. Use Promise.all for independent tasks, Promise.allSettled when you need every result even if some fail, and Promise.race for timeouts.

Myths to avoid

• Myth: await blocks the entire Node process. Reality: only that async function's continuation waits.
• Myth: async functions run on a new thread. Reality: still the same event-loop thread unless you use worker threads.
• Myth: .then is obsolete. Reality: it is still useful for concise pipelines and library APIs.

A crisp interview answer

async/await is Promise syntax that makes asynchronous code read like synchronous code. I use await with try/catch for sequential steps and Promise.all when work is independent. I am careful to await every Promise so errors do not become unhandled rejections.