Remember the dial-up days when pages took half a minute to load? Most often, JavaScript is the culprit - or more specifically, how we use it. Today we'll explore proper code optimization techniques and share working solutions for common performance issues.
Key takeaways 👌
Smart code optimization can speed up website loading by 60-70% without losing functionality
Asynchronous loading of scripts cuts the time to first render in half
Lazy loading of images and scripts significantly improves performance - loading time decreases by 30-40%
Introduction
Remember those old computer games that lagged even on powerful machines? Often it wasn't the hardware but the code. The same thing happens with modern websites – even a super-powerful server won't save you if your JavaScript is poorly optimized.
Today, the average JavaScript code size on websites reaches 350 KB, and it's only growing. Studies show that about 40% of this code is never used during page load. Every extra kilobyte means additional loading time, especially on mobile devices and slow internet connections.
Interesting fact 👀
Did you know that JavaScript was created in just 10 days? Brendan Eich was tasked with "making something like Java, but simpler." Now this 10-day project runs the internet. It's like writing a song in one evening, and then it becomes a global hit!
Practical optimization tips
Code optimization is like packing a large suitcase for travel. There are several proven ways to make your baggage lighter:
- Remove the unnecessary. Remember how mom taught you to pack for trips? "Only take what you need!" Same goes for JavaScript – every extra line of code means additional milliseconds of loading time. Code name example
// Before: function loadUserData(user) { console.log('Checking data'); console.log('Loading...'); return user.name; } // After: function loadUserData(user) { return user.name; } - Load smartly. Put essential items on top, the rest at the bottom. In code, we use async and defer: Code name example
// Core scripts - immediately <script src="core.js"></script> // Secondary loads later <script async src="stats.js"></script> <script async src="stats.js"></script>
The most complex performance issues often have simple solutions. Sometimes just properly placing async and defer on your scripts can make your site load twice as fast. It's not about complex optimizations, but understanding the basics
Lazy loading
Imagine a restaurant where the chef prepares all dishes in advance - some might go bad, and the kitchen is always chaotic. A smart chef cooks as orders come in.
// Load heavy functionality
// only when needed
button.addEventListener(
'click',
async () => {
const { heavyF } = await import(
'./heavy-f.js'
);
heavyF();
}
);JavaScript today is the foundation of the web. But like in building a house, it's not just about the material, but how you use it. Unoptimized code can turn a Ferrari into a rusty old junker.
— Dan Abramov, creator of Redux and React developer
DOM and how to work with it
Working with the DOM often becomes a performance bottleneck. Here's a classic example of inefficient code you might find on many websites:
// Common mistake when working with DOM
for (let i = 0; i < 100; i++) {
document.body.innerHTML += 'Block';
}
// Optimized version
const container = document.createDocumentFragment();
for (let i = 0; i < 100; i++) {
container.appendChild(document.createElement('div'));
}
document.body.appendChild(container);
Check out our article What is Web 3.0 and what it means for Internet evolution, where we dive deep into how the Web 3.0 standard is changing approaches to web application performance
Recommended reading 🤓
"JavaScript: The Good Parts", Douglas Crockford
If Douglas Crockford wrote a cookbook, this would be it. Only the tastiest JavaScript recipes.
On Amazon
"Eloquent JavaScript", Marijn Haverbeke
Marijn Haverbeke wrote this book as if he's telling an interesting story rather than teaching programming.
On Amazon
"High Performance JavaScript", Nicholas C. Zakas
The go-to book for those who want their code to fly, not crawl.
On AmazonConclusion
JavaScript optimization isn't a one-time task – it's an ongoing process of improvements. Start with simple steps: remove unused code, set up proper script loading, implement lazy loading. Each small improvement adds up to a significant performance boost.
Artyom Dovgopol
Code optimization is an art form. It's like racing: you can just hop in and drive, or you can tune every part of the engine. The difference is obvious right away 😉