# Promise vs Async/Await

URL: https://softwaredictionary.org/compare/promise-vs-async-await
Last updated: 2026-10-06

In short: A promise is an object for a value that arrives later; async/await is syntax built on promises that lets you wait for them in step-by-step code.

## What is the difference between a promise and async/await?

A promise is an object that stands for the result of an asynchronous operation: it starts pending and later becomes fulfilled with a value or rejected with an error. Async/await is syntax for using promises: an `async` function always returns a promise, and inside it `await` pauses the function until a promise settles, then hands back its value or throws its error.

So they are not rivals; async/await is another way of writing the same thing. With promises alone, you chain a `.then()` for each step and end with a `.catch()` for errors. With async/await, the same steps read top to bottom like ordinary code, local variables stay in scope from one step to the next, and errors are handled with a regular `try/catch`.

You still use promises directly in async code. Running independent tasks at once needs `Promise.all`, `Promise.allSettled` or `Promise.race`, and wrapping an old callback or event API takes `new Promise`. A common mistake is awaiting independent calls one after another, which makes them run in sequence; start them together and await them with `Promise.all` instead.

Another misconception is that `await` blocks the program. It pauses only the async function it is in; the event loop keeps handling clicks, timers and other requests in the meantime. Both styles perform the same, so the choice is about readability: async/await for sequences of steps, promise methods for combining several operations.

| Aspect | Promise | Async/Await |
| --- | --- | --- |
| What it is | An object that represents a future value | Syntax for writing promise-based code |
| Code style | A chain of `.then()` callbacks | Step-by-step code with `await` |
| Errors | `.catch()` at the end of the chain | `try/catch` around the awaited steps |
| Returns | A new promise from every `.then()` | A promise from every `async` function |
| Running in parallel | `Promise.all`, `Promise.race` and similar helpers | Still uses `Promise.all`; plain `await` runs steps in order |
| Debugging | Harder to step through across many callbacks | Steps through like synchronous code |
| Added to JavaScript | ES2015 | ES2017 |

## Choose Promise when

- You run several operations at once and combine them with `Promise.all` or `Promise.race`.
- You wrap a callback- or event-based API in `new Promise` so it can be awaited.
- A short, one-step chain reads clearly enough on its own.

## Choose Async/Await when

- The code is a sequence of steps that depend on each other.
- You want to handle errors with ordinary `try/catch` blocks.
- You need loops or conditions between asynchronous steps.

## Frequently asked questions

**Is async/await better than promises?**

It is easier to read for most sequential code, but it is not a replacement: it is built on promises and uses them underneath. Most modern code mixes both, with `await` for steps and `Promise.all` for parallel work.

**Is async/await slower than promises?**

No meaningful difference. Both run on the same promise machinery; the real slowdown comes from awaiting independent tasks one by one instead of together.

**Can I await any promise?**

Yes. `await` works with any promise, or any object with a `then` method, including promises returned by libraries written before async/await existed.

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Software Dictionary: https://softwaredictionary.org/ · https://softwaredictionary.org/llms.txt