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10 Ways to Optimize JavaScript Code Performance

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Optimize JavaScript Code Performance

JavaScript is a key language for web development, but with growing applications, its performance is of great significance. Optimize JavaScript code performance improves the speed and efficiency of your applications. According to Google, 53% of mobile users leave a site that takes longer than 3 seconds to load. Moreover, Akamai’s survey found that conversion rates can decrease by 7% just because website load time was delayed by only 100 milliseconds. This means that JavaScript performance should be focused on so as to improve speed and enhance user experience, as well as possibly increase conversions.

1. Understand JavaScript Performance


JavaScript engines such as V8 (used in Chrome) and SpiderMonkey (used in Firefox) are highly optimized, but having some knowledge about how they work will help you write faster code.

  1. JIT Compilation – At runtime, JavaScript engines use Just-In-Time (JIT) compilation to convert JavaScript into machine code. Optimizing the code becomes better if it has more predictability.
  2. Garbage Collection – Memory that is no longer used is automatically freed up through this process. Time taken during garbage collection can be reduced by having effective memory management.

2. Profiling and Benchmarking

it is very important to identify where the bottlenecks are before optimizing Javascript code. Profiling and benchmarking tools are useful and play an important role.

Chrome DevTools: Examine the runtime performance of your app using the Performance panel. Here is how to get started:

  1. Open Chrome DevTools (right click on your page and choose “Inspect”).
  2. Switch to “Performance” tab.
  3. Press “Record” and enact the actions you want to profile.
  4. Click “Stop” for the recording to finish and see performance data.

function exampleFunction() {  
    for (let i = 0; i < 1000000; i++) {  
        // Simulate a heavy task  
    }  
}  
exampleFunction();


While exampleFunction is running, record its performance and calculate the time taken.

Lighthouse: An inbuilt tool within Chrome DevTools for auditing web pages.

  1. Start Chrome DevTools.
  2. Select the “Lighthouse” tab.
  3. Click on “Generate Report” to execute an audit.

Benchmark.js: A JavaScript library that measures the execution speed of your code.

const Benchmark = require('benchmark');  
const suite = new Benchmark.Suite;  

suite.add('Example', function() {  
    for (let i = 0; i < 1000000; i++) {  
        // Simulate a heavy task  
    }  
})  
.on('cycle', function(event) {  
    console.log(String(event.target));  
})  
.on('complete', function() {  
    console.log('Fastest is ' + this.filter('fastest').map('name'));  
})  
.run({ 'async': true });

3. Optimizing Loops and Iterations

Loops are often a major cause of inefficiency. Below are a few tips on how you can optimize them:

// Inefficient way to write loops  
for (let i = 0; i < items.length; i++) {  
    process(items[i]);  
}  

// Efficient way write loops 
const length = items.length;  
for (let i = 0; i < length; i++) {  
    process(items[i]);  
}  
items.forEach(item => process(item));

4. Efficient DOM Manipulation

Manipulating the DOM entails some of the most expensive operations in JavaScript. For better performance, minimize these operations as much as possible.

const fragment = document.createDocumentFragment();  
items.forEach(item => {  
    const element = createElement(item);  
    fragment.appendChild(element);  
});  
document.body.appendChild(fragment);

5. Event Handling Best Practices


For a responsible application, it is necessary to have effective event handling.

document.body.addEventListener('click', event => {  
    if (event.target.matches('.item')) {  
        handleItemClick(event);  
    }  
});
function debounce(func, wait) {  
    let timeout;  
    return function(...args) {  
        clearTimeout(timeout);  
        timeout = setTimeout(() => func.apply(this, args), wait);  
    };  
}  

const handleResize = debounce(() => {  
    console.log('Window resized');  
}, 200);  

window.addEventListener('resize', handleResize);

6. Memory Management Techniques


Efficient memory management helps avoid leaks and ensures smooth performance.

const weakMap = new WeakMap();  
const obj = {};  
weakMap.set(obj, 'value');

7. Lazy Loading and Code Splitting

Increase performance by only loading code resources when required.

<img src="placeholder.jpg" data-src="actual-image.jpg" class="lazy-load">
import(/* webpackChunkName: "myChunk" */ './myModule').then(module => {  
    module.doSomething();  
});

8. Using Web Workers for Parallel Processing


Web Workers give you the ability to run scripts in background threads, thus freeing up the main thread which results in better performance.

const worker = new Worker('worker.js');  
worker.postMessage('start');  

worker.onmessage = function(event) {  
    console.log('Message from worker:', event.data);  
};


Web Workers are useful for CPU-intensive tasks like data processing and complex calculations.

9. Leveraging Modern JavaScript Features

Modern JavaScript (ES6+) has some improvements that can be beneficial to your code’s optimization.

const add = (a, b) => a + b;  
const { name, age } = person;
async function fetchData() {  
    const response = await fetch('https://api.example.com/data');  
    const data = await response.json();  
    console.log(data);  
}

10. Other Important Areas

Minimize HTTP Requests

Minify and Compress Code

Efficient Use of Caching

Don’t Block the Main Thread

<script src="script.js" async></script>  
<script src="script.js" defer></script>

11. Best Practices for Writing Efficient JavaScript Code

Conclusion

Optimizing JavaScript performance is a continuous process involving multiple strategies. These are all areas mentioned in this guide, plus some other techniques which provide a comprehensive approach towards making JavaScript apps faster as well as more efficient.

If these best practices above are adhered to alongside utilization of available tools and techniques then not only will your javascript code be performant but also scalable.

References

Footnotes

  1. Google. “Find Out How You Stack Up to New Industry Benchmarks for Mobile Page Speed.” https://www.thinkwithgoogle.com/marketing-strategies/app-and-mobile/mobile-page-speed-new-industry-benchmarks/ ↩ 
  2. Google Developers. “Lighthouse.” https://developers.google.com/web/tools/lighthouse ↩
  3. Benchmark.js. “Benchmark.js Documentation.” https://benchmarkjs.com/ ↩
  4. React Documentation. “Virtual DOM.” https://reactjs.org/docs/faq-internals.html ↩

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