Q229- What are promises and difference b/w async/await and promises.

A Promise in JavaScript represents a value that will be available in the future.
It is used to handle asynchronous operations like API calls, timers, file reads, etc.

A Promise has 3 states:

1. Pending – waiting for the result
2. Fulfilled – operation completed successfully
3. Rejected – operation failed

Example:

const fetchData = new Promise((resolve, reject) => {
  const success = true;

  if (success) {
    resolve("Data loaded");
  } else {
    reject("Error loading data");
  }
});

fetchData
  .then(res => console.log(res))
  .catch(err => console.log(err));

---

⭐ Difference Between Promises and async/await

Both are used for asynchronous programming, but async/await is built on top of Promises.

---

✅ 1. Syntax & Readability

Promises

fetchUser()
  .then(data => process(data))
  .then(result => console.log(result))
  .catch(err => console.error(err));

❌ Can become messy → “Promise chaining”

async/await

async function loadUser() {
  try {
    const data = await fetchUser();
    console.log(data);
  } catch (err) {
    console.log(err);
  }
}

✔ Looks like synchronous code
✔ Cleaner and easier to understand

---

✅ 2. Error Handling

Promises

Errors handled using .catch()

fetchData()
  .then(res => console.log(res))
  .catch(err => console.log(err));

async/await

Errors handled using try...catch (more readable)

try {
  const res = await fetchData();
} catch (err) {
  console.log(err);
}

---

✅ 3. Under the Hood

• Promises work using .then(), .catch(), .finally()
• async/await is syntactic sugar on top of Promises
• Every await returns a Promise

async function test() {
  return "Hello"; 
}
test().then(res => console.log(res)); // "Hello"

✔ async functions always return a promise

---

✅ 4. Async Flow Control

Promises:

Best for running tasks in parallel using:

Promise.all()
Promise.race()
Promise.allSettled()

async/await:

Best for sequential step-by-step operations.

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📌 5. Which One Should You Use?

Use async/await when:

• You want cleaner code
• You have sequential operations
• You want easier error handling

Use Promises when:

• You need parallel async tasks
• You need Promise utilities (all, race, etc.)

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💡 In Short:

Promises

• Asynchronous operations
• Uses .then() and .catch()
• Good for parallel tasks

async/await

• Cleaner syntax
• Built on Promises
• Uses try/catch
• Better readability