Async Wait

In JavaScript, the async keyword is used to define a function that always returns a Promise and allows the use of await within its body to pause execution until a Promise settles.

What async Does

• Placing async before a function declaration ensures that the function returns a Promise, even if it appears to return a plain value

• Example:

  javascriptasync function myFn() { return "Hello"; } *// Equivalent to:* function myFn() { return Promise.resolve("Hello"); }

• The actual return value is always wrapped in a resolved Promise, unless an error is thrown, in which case the Promise is rejected

Using await Inside async Functions

• The await keyword can only be used inside an async function

• await pauses the function execution until the awaited Promise resolves, then resumes execution and returns the resolved value.

• Example:

  javascriptasync function fetchData() { const response = await fetch("<https://jsonplaceholder.typicode.com/posts/1>"); const data = await response.json(); console.log(data); } fetchData();

• This way, asynchronous code reads more like synchronous code, making it easier to understand and maintain.

Key Points

• Async functions simplify working with Promises by making asynchronous logic appear synchronous
• They always return a Promise, which can be used with .then or caught with .catch (or via try..catch inside the function).
• Allows for improved error handling and linear, readable asynchronous code flow.

Example Patterns

• Sequential, parallel, and concurrent execution using async/await enables various asynchronous control flows:
  • Sequential: Wait for each operation before starting the next.
  • Parallel: Launch multiple operations, then wait for all using Promise.all and await.

Async functions and the await keyword are fundamental for modern JavaScript development, especially when handling I/O, APIs, and other asynchronous tasks.

Async functions in JavaScript differ from regular functions mainly in their return value and their ability to pause execution to wait for asynchronous operations using await