JavaScript Promises vs Async/Await Explained

By Sarah Chen Jul 11, 2026 8 min read Programming

JavaScript handles asynchronous operations through callbacks, promises, and async/await. Here is how promises and async/await compare.

Understanding Promises

A Promise represents a value that might be available now, later, or never. It has three states: pending, fulfilled, or rejected. You handle results with .then() and errors with .catch(). Promises support chaining for sequential operations and Promise.all() for parallel operations.

Understanding Async/Await

Async/await is syntactic sugar over promises. An async function returns a promise. The await keyword pauses execution until the promise settles. This makes asynchronous code look synchronous, improving readability. Error handling uses try/catch blocks instead of .catch().

Key Differences

Promises use chaining (.then().catch()), while async/await uses sequential code with try/catch. Async/await is generally more readable for complex flows. Promises are better for simple callbacks. Promises support Promise.all(), Promise.race(), and Promise.allSettled() naturally, while async/await requires wrapping these.

Error Handling

Promises handle errors with .catch() at the end of the chain. Any error in the chain is caught by the final .catch(). Async/await uses try/catch blocks. A single try/catch can wrap multiple awaits. Unhandled promise rejections in async functions are caught by the caller's try/catch.

Parallel Execution

For parallel operations, use Promise.all() with both patterns. With promises: Promise.all([fetchA(), fetchB()]).then(). With async/await: const [a, b] = await Promise.all([fetchA(), fetchB()]). Both achieve the same result.

Which Should You Use?

Use async/await for most new code due to better readability. Use promises directly for simple callbacks, when you need to pass promises as values, or for compatibility with older codebases. You can mix both since async/await is built on promises.