What is await?

Await is a keyword used in asynchronous programming (most commonly in JavaScript and TypeScript) that tells the program to pause the execution of an async function until a Promise settles (either resolves with a value or rejects with an error). While the function is paused, other code can keep running, so the program stays responsive.

Let's break it down

  • An async function is a special kind of function that always returns a Promise.
  • Inside an async function you can write await somePromise.
  • When the interpreter reaches await, it temporarily stops running that function and hands control back to the event loop.
  • Once somePromise finishes, the function resumes right after the await line, and the resolved value becomes the result of the await expression.
  • If the Promise rejects, the error can be caught with a normal try...catch block.

Why does it matter?

Await makes asynchronous code look and behave like regular, step‑by‑step code. This improves readability, reduces the need for deeply nested callbacks, and lets developers handle errors with familiar try...catch syntax. It helps avoid “callback hell” and makes it easier to reason about the order of operations.

Where is it used?

  • In web browsers for tasks like fetching data (await fetch(...)).
  • In Node.js for file I/O, database queries, network requests, and more.
  • In TypeScript, which compiles to JavaScript, the same syntax applies.
  • In other languages that support similar concepts, such as C# (async/await) and Python (async/await).
  • Anywhere you need to work with Promises or other asynchronous operations.

Good things about it

  • Clear syntax: Code reads top‑to‑bottom, just like synchronous code.
  • Simplified error handling: Use try...catch instead of .catch() chains.
  • Better debugging: Stack traces are easier to follow because the flow is linear.
  • Integration with existing APIs: Works seamlessly with any function that returns a Promise.
  • Improves maintainability: Less nesting means fewer bugs and easier updates.

Not-so-good things

  • Only inside async functions: You can’t use await at the top level of a script (unless the environment supports top‑level await).
  • Potential performance hit: Overusing await in loops can serialize operations that could run in parallel, slowing things down.
  • Hidden concurrency: Because the function appears to pause, developers might forget that other code is still running, leading to race conditions if not careful.
  • Error propagation: If a Promise rejects and you forget a try...catch, the error can bubble up and crash the async function.
  • Browser compatibility: Older browsers need transpilation (e.g., Babel) to support async/await.