JavaScript Promises and Async/Await

Promises

• JavaScript's Promise.all handles multiple promises concurrently.
• Promise.all takes an array of promises as input and returns a single promise.
• The returned promise resolves only when all input promises resolve.
• If any input promise rejects, the returned promise immediately rejects.
• Resolved values of all promises (if the returned promise resolves) are returned in an array.
• Promise.allSettled() returns an array of objects. Each object has a "status" (fulfilled or rejected) and the corresponding value or reason for each promise. It waits for all promises to settle, unlike Promise.all which rejects immediately if one promise rejects.

Async/Await

• Async/await simplifies asynchronous operations.
• The async keyword designates a function as asynchronous.
• An async function returns a promise.
• The await keyword pauses execution until a promise resolves inside an async function.
• Only use await inside an async function.
• await causes the JavaScript engine to pause execution of the async function until the promise is either fulfilled or rejected and return the result instead of using then chains. If it is rejected, an error is thrown.