Q46- Explain JavaScript promises and async/await

A Promise in JavaScript is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value.
async/await is syntactic sugar on top of promises that allows writing asynchronous code in a synchronous-like manner.

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🔹 Promises

• A promise can be in three states:
  1. Pending → initial state, neither fulfilled nor rejected
  2. Fulfilled → operation completed successfully
  3. Rejected → operation failed

Example:

const fetchData = new Promise((resolve, reject) => {
  const success = true; 
  setTimeout(() => {
    if (success) resolve("Data received!");
    else reject("Error occurred");
  }, 1000);
});

fetchData
  .then(data => console.log(data))   // "Data received!"
  .catch(error => console.log(error));

• .then() handles success, .catch() handles failure, and .finally() executes regardless.

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🔹 Async/Await

• async function always returns a promise.
• await pauses execution until the promise resolves or rejects.

Example:

function getData() {
  return new Promise((resolve) => {
    setTimeout(() => resolve("Hello World"), 1000);
  });
}

async function fetchData() {
  try {
    const result = await getData();
    console.log(result); // "Hello World"
  } catch (error) {
    console.log(error);
  }
}

fetchData();

• Makes asynchronous code look linear and easier to read.
• Still uses Promises under the hood.

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✅ Key Points

• Promises help avoid callback hell.
• async/await is cleaner for sequential asynchronous operations.
• Use Promise.all() to run multiple promises in parallel.