Mastering the Event Loop in JavaScript

The Event Loop is a fundamental concept for modern JavaScript development. It allows asynchronous operations to be handled efficiently.

1. The Call Stack

The call stack is where your functions get executed in order. If a function calls another function, it's pushed onto the stack.

2. The Task Queue (Macrotasks)

Macrotasks include setTimeout, setInterval, and I/O operations. They wait for the stack to be empty before execution.

3. The Job Queue (Microtasks)

Microtasks include Promises and MutationObservers. These run before the next macrotask.

4. Practical Example

console.log('Start');
setTimeout(() => console.log('Timeout'), 0);
Promise.resolve().then(() => console.log('Promise'));
console.log('End');

Output: Start → End → Promise → Timeout

Conclusion

Understanding the event loop helps prevent unexpected behavior and improves performance.