What is the Event Loop in JavaScript?

What You'll Learn

• How the event loop works
• Microtasks vs macrotasks
• Execution order

What is the Event Loop?

The event loop allows JavaScript to perform non-blocking operations despite being single-threaded.

How It Works

1. Execute synchronous code in the call stack
2. Check microtask queue (Promises)
3. Check macrotask queue (setTimeout, setInterval)
4. Repeat

Example

console.log('1');

setTimeout(() => console.log('2'), 0);

Promise.resolve().then(() => console.log('3'));

console.log('4');

// Output: 1, 4, 3, 2

Why This Order?

• 1, 4: Synchronous code runs first
• 3: Microtasks (Promises) run next
• 2: Macrotasks (setTimeout) run last