Tips to Improve performance in JavaScript


According to GitHub, JavaScript is the most popular language amongst developers even in Q2, 2021. With such massive popularity, the competition is fierce, and it becomes crucial for JavaScript developers to stay updated with best performance practices. This blog introduces you to 12 best practices for improving JavaScript performance in your web applications.

12 Ways to Improve JavaScript Performance in Web Apps 

Learn Asynchronous Programming

Since your application needs several internal calls to several APIs, it may block the application since Javascript has many synchronous components and is single-threaded. However, you can use Javascript’s async.js feature to manage asynchronous codes efficiently. However, there’s still a scope that the application uses an external library, which could revert to the synchronous blocking and affect application performance. 

You can deal with this by using asynchronous APIs throughout the code. Though it may be difficult for inexperienced individuals to learn, experienced developers can carry it well. 

Define Variables Locally

  • Local variable – Variables defined within the functions 
  • Global Variable – Variables that can be accessed globally throughout the script

There are two types of variables. 

Whenever a function is called, the browser starts looking for the variables defined throughout the script. The activity is termed “scope lookup.” If the variables declared in the function are outside the current scope, it takes more time for the engine to search and hence, slows down the application. Thus, variables defined locally boost overall application speed. 

Use HTTP/2

The latest version of the HTTP protocol, HTTP/2, has some good enhancements that speed up the overall website by improving the Javascript performance. In addition, it uses multiplexing to allow multiple requests and responses to be sent at the same time. Moving from HTTP to HTTPS, you can take advantage of those performance improvements in HTTP/2.

Use Pointer Reference

Refreshing the DOM multiple times slows down the website loading speed. You can eliminate this by storing pointer references of in-browser objects. Storing a reference to DOM or jQuery objects is one of the best ways to speed up your website. For example, if you need to do iterations inside a function, you can make a local variable with a pointer reference to the object.

Batch and Buffer your DOM

Instead of reloading the DOM after each iteration, it is advisable to batch the small changes into one to prevent unnecessary screen rendering. For example, all the style-related modifications need to be done at once rather than applying them individually. 

For scrollable DIVs, use a buffer to remove the items from the DOM that aren’t visible inside the viewport. This technique helps to save both memory usage and DOM traversal.

Event Delegation Implementation

Large web applications come with multiple event handlers, creating chaos in the absence of event delegation. Event delegation streamlines the use of a single event handler for efficient management of a specific type of event for the entire page. Less functionality, lower memory usage, and fewer ties between DOM and your code are a few of the many perks of using event delegation. 

Boost Performance By Caching in The Browser

Improve Javascript performance by storing a repeated access object inside a user-defined variable or using a variable to refer to that object.

You can either use JavaScript Cache API that can be leveraged by installing a service worker or HTTP protocol cache to do this. 

Avoid Unwanted Loops

Having too many loops in JavaScript is not considered ideal as it puts too much strain on the browser. Instead, try to minimize your loop size. The lower the loop size, the faster the loop. Simple tricks can assist you in achieving efficiency, like storing the array’s length in a separate variable instead of reading the length after each iteration of the loop. 

Eliminate Memory Leaks

If there is an ongoing memory leak, the loaded page keeps on reserving memory, eventually hindering the performance by occupying all the available memory devices. This type of failure is likely to be seen on a page with an image carousel or slider. To fight this problem, analyze your website’s memory leaks in chrome dev tools by recording a timeline in the performance tab. 

Limit Library Dependencies

Being dependent on libraries means they need to load each time you call the function. This contributes to a lot of loading time – the more libraries, the more time it takes to load. To reduce the dependency on external libraries, you can resort more to in-browser technologies. Furthermore, if you need complex CSS selectors, instead of relying on jQuery, try using Sizzle.js.

Get rid of Unused Code

Before rendering the DOM, the browser compiles the code and based on the complexity, it takes more time to render. For example, while coding, we often declare numerous variables that we never use in our code. Therefore, detaching functions not being used by any of the users is another way of improving the website’s load times. 

Use Tools For Improving Performance

Have some assistance from numerous tools available in the market to make your website’s performance blazing fast. 

There are several tools available like…

  • Lighthouse – A tool that helps in performance audits, SEO, etc. 
  • Google PageSpeed – To help JavaScript developer looks for areas of improvement.
  • NodeSource platform – for granular performance exploration of all the apps built on Node.js
  • Google Closure Compiler – for analyzing and rewriting code for optimal performance. It also double-checks for syntax errors and variable references.


There are multiple ways to boost your application performance through Javascript, and this list has some of them to help you optimize the loading time and boost performance. Try these out and see how it changes your application experience and also, let us know the tips that helped you the most in the comment section below.