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How to improve JavaScript performance?

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Sep 12, 2023 pm 12:25 PM

How to improve JavaScript performance?

In today’s world, almost every website uses JavaScript. Web applications are becoming more complex and user interactive, which leads to performance issues. It leads to a bad user experience, which is undesirable for any web application. Different factors can cause poor performance, long loading times, and long response times.

In this tutorial, we will discuss all these factors and how to solve this problem and improve the performance of JavaScript.

Lightweight and compact code

The first thing you can do to improve JavaScript performance is to write lightweight, compact code. JavaScript code can have multiple modules and some unused functions or variables, which can be easily removed from the code. It will improve JavaScript compilation time, resulting in better performance. Additionally, using advanced algorithms to perform complex tasks can be very beneficial for improving performance.

Use local variables

JavaScript accesses local variables faster than global variables, so using local variables can improve JavaScript performance. Whenever we access a variable, JavaScript first searches for the variable in the local scope and then looks for global variables. If all variables are defined in local scope, it will reduce the time to access it. Furthermore, local variables are destroyed after the function call is completed, but global variables retain their values in memory. This can also cause memory issues.

// Local variables
const id = 10
let value = 'Tutorialspoint'
// Global variables
var key = 'JavaScript'

Reduce DOM access

Accessing the DOM and manipulating it is one of the most important functions of JavaScript. But too many unnecessary accesses to the DOM can cause huge performance issues. Whenever we manipulate an element in the DOM, the DOM is refreshed with an updated state, and if you keep updating the DOM elements every second, the DOM is refreshed every second. So it is recommended to update the DOM when necessary. If the user needs to update an element multiple times, it's better to store the element object in a variable and use that variable to update the DOM.

let element = document.getElementById('element_id')
element.innerHTML = 'Tutorialspoint'

Reduce the number of loop iterations

Loops are a simple way to accomplish some repetitive tasks, but they can also lead to poor performance. Long iteration loops take a lot of time to complete, so it's best to avoid using long loops if possible. Instead, use small loops and perform minimal tasks within the loop. Also, don't access the DOM in a loop; this will cause huge performance issues since you're manipulating the DOM on every loop iteration.

let names = ['abc', 'xyz', 'mno', 'pqr'];
let element = document.getElementById('element_id');
// DON’T DO THIS
for(let index=0; i<names.length; i++){
   element.innerHTML += names[index] + ' ';
}
// DO THIS
let str = '';
for(let index=0; i<names.length; i++){
   str += names[index];
}
element.innerHTML = str;

Using asynchronous programming

Asynchronous programming is one of the best ways to improve web application performance. In asynchronous programming, code execution is done asynchronously, so multiple tasks can be performed simultaneously. It results in fast loading of data and fast response. In JavaScript, asynchronous operations are performed by AJAX, which stands for Asynchronous Javascript and XML.

let http = new XMLHttpRequest()
http.open('GET', '...URL')
http.onload = function(){
   console.log(this.response); // the response
}

Place JavaScript at the bottom of the page

When JavaScript is placed at the top of the page, it executes when the page loads, so it takes some extra time to load the entire page. It causes pages to load slowly. To solve this problem, JavaScript should be placed at the bottom of the page so that JavaScript starts executing after the entire page is loaded.

Example

<html>
<body>
   <div>Your Page Content</div>
   <div id='element'></div>
   <script>
      // JavaScript Code at Page's Bottom
      document.getElementById('element').innerHTML = 'Welcome to
      Tutorialspoint'
   </script>
</body>
</html>

Eliminate memory leaks

If a web application has a memory leak, then the application will allocate more and more memory, causing huge performance and memory problems. To resolve this issue, make sure there are no memory leaks in your application and check if variables are not taking too many values. Users can observe memory leaks in Chrome development tools.

Use optimization algorithm

Complex tasks in JavaScript generally take a lot of time, which can lead to performance issues, and using optimized algorithms; we can reduce the time required to perform tasks. Rewrite the algorithm in a more optimized way to get the best results. Also, avoid using long loops, recursive calls, and global variables.

Creating and using variables

In JavaScript, only create variables that you will use and hold values. Use the following and avoid unnecessary lines of code and variable declarations -

document.write(num.copyWithin(2,0));

Avoid using with

with keyword does not have a good impact on JavaScript speed. Avoid using it in your code.

Faster Loops

When using loops, keep assignments outside the loop. This will make the loop faster -

var i;
// assignment outside the loop
var j = arr.length;
for (i = 0; i < j; i++) {
   // code
}

Use other tools to find problems

Your web application seems to be working fine, but there may be some performance issues, and in order to identify these issues, some tools may be useful. Lighthouse is a useful web application performance analysis tool. It helps check performance, best practices, accessibility, and SEO. Not only this tool is available on the internet, but there are other tools that can be used to check the performance of web applications and we can simply see the problems and try to overcome them.

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