Q84- What are generators and how are they different from async functions?

Generators and async functions are both special functions in JavaScript that handle paused and resumed execution, but they serve different purposes and work differently.

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1️⃣ Generators

• Declared with function* syntax
• Can pause execution with yield and resume later
• Useful for lazy iteration or custom iterators
• Returns an iterator object with next() method

function* genNumbers() {
  yield 1;
  yield 2;
  yield 3;
}

const gen = genNumbers();

console.log(gen.next()); // { value: 1, done: false }
console.log(gen.next()); // { value: 2, done: false }
console.log(gen.next()); // { value: 3, done: false }
console.log(gen.next()); // { value: undefined, done: true }

✅ Key points:

• Execution pauses at yield
• Manual control with next()
• Synchronous by default (does not handle Promises automatically)

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2️⃣ Async Functions

• Declared with async keyword
• Always return a Promise
• Execution pauses at await until the Promise resolves
• Makes asynchronous code look synchronous

async function fetchData() {
  const res = await fetch("https://api.example.com/data");
  const data = await res.json();
  return data;
}

fetchData().then(console.log);

✅ Key points:

• Handles async operations automatically
• No manual next() calls
• Execution pauses only at await

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3️⃣ Key Differences

Feature	Generator	Async Function
Syntax	function*	async function
Returns	Iterator	Promise
Execution	Paused/resumed with yield + next()	Paused/resumed automatically with await
Purpose	Lazy iteration, custom iterators	Asynchronous programming (API calls, timers)
Handling Promises	Manual (can yield Promises)	Automatic, waits for Promise resolution

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4️⃣ Example Comparison

Generator:

function* asyncGen() {
  const a = yield Promise.resolve(1);
  const b = yield Promise.resolve(2);
  return a + b;
}

• Must manually handle each yield value with .next()

Async Function:

async function asyncFunc() {
  const a = await Promise.resolve(1);
  const b = await Promise.resolve(2);
  return a + b;
}

• Automatically waits for Promises, much simpler

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⚡ In short:

Generators are for synchronous control flow and lazy iteration, manually paused with yield.
Async functions are for asynchronous operations, automatically pausing at await and returning a Promise.

Generators give manual control, async functions give automatic async handling.