Mastering the Event Loop for High-Performance JavaScript

JavaScript’s single-threaded nature doesn’t mean slow performance. The event loop is key to understanding and optimizing JS apps.

Event Loop 101

Call Stack: Executes synchronous code
Task Queue: Holds callbacks (setTimeout, I/O)
Microtask …


This content originally appeared on DEV Community and was authored by Sarva Bharan

JavaScript's single-threaded nature doesn't mean slow performance. The event loop is key to understanding and optimizing JS apps.

Event Loop 101

  1. Call Stack: Executes synchronous code
  2. Task Queue: Holds callbacks (setTimeout, I/O)
  3. Microtask Queue: Promises, queueMicrotask()
  4. Event Loop: Orchestrates execution 
console.log('1');
setTimeout(() => console.log('2'), 0);
Promise.resolve().then(() => console.log('3'));
console.log('4');
// Output: 1, 4, 3, 2

Performance Pitfalls

  1. Long-running tasks block the loop
  2. Excessive DOM manipulation
  3. Synchronous network requests

Optimization Techniques

  1. Use async/await for cleaner asynchronous code 
async function fetchData() {
  const response = await fetch('https://api.example.com/data');
  return response.json();
}
  1. Debounce expensive operations 
const debounce = (fn, delay) => {
  let timeoutId;
  return (...args) => {
    clearTimeout(timeoutId);
    timeoutId = setTimeout(() => fn(...args), delay);
  };
};
  1. Use Web Workers for CPU-intensive tasks 
const worker = new Worker('heavy-calculation.js');
worker.postMessage({data: complexData});
worker.onmessage = (event) => console.log(event.data);
  1. Virtualize long lists
  2. Use requestAnimationFrame for smooth animations
  3. Batch DOM updates

Measuring Performance

  1. Use Performance API 
performance.mark('start');
// Code to measure
performance.mark('end');
performance.measure('My operation', 'start', 'end');
  1. Chrome DevTools Performance tab
  2. Lighthouse audits

Remember: The fastest code is often the code not written. Optimize wisely.

Cheers🥂


This content originally appeared on DEV Community and was authored by Sarva Bharan


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