March 3, 2024

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10 JavaScript Tips and Tricks to Optimize Performance

10 JavaScript Tips and Tricks to Optimize Performance

JavaScript is vital for web development. The language is behind most of the interactivity and animation you’ll see on websites. But JavaScript can also cause a website to slow down if the code is poorly written. Inefficiencies can result in both poor loading times and slow rendering speed.

Adopt the following practices to improve the speed and performance of your website.


1. Define Variables Locally

As a programmer, you need to know how scoping works. There are two types of variables in JavaScript: local variables and global variables.

Local variables are variables declared within a function block. The scope remains within the function only in which they’re declared. Global variables are variables accessible throughout the script. In the case of global variables, the scope remains throughout the program.

Whenever you try to access a variable, the browser does something known as a scope lookup. It checks the nearest scope for the variable and keeps looking up until it finds the variable. Thus, the more scope chain you have in your program, the longer it’ll take to access variables beyond the current scope.

For this reason, it’s best to always define your variables closer to the execution context. Only use global variables on rare occasions; when you want to store data used throughout the script, for example. This will reduce the number of scopes in your program, thereby improving performance.

2. Load JavaScript Asynchronously

A diagram showing 3 queued, sleeping processes an 1 active process that the CPU is currently running

JavaScript is a single-threaded programming language. This means that once a function executes, it has to run till the end before another function can run. This architecture can lead to situations in which code can block the thread and freeze the app.

To keep the thread performing well, you should run certain time-wasting tasks asynchronously. When a task runs in asynchrony, it doesn’t take up all of the thread’s processing power. Instead, the function joins an event queue where it’s fired after the execution of all other codes.

API calls are perfect for the asynchronous pattern because they take time to resolve. So instead of having it hold up the thread, you’d use a promise-based library like the fetch API to fetch the data asynchronously. That way, other code can run while the browser retrieves data from the API.

Understand the intricacies of asynchronous programming and you’ll improve the performance of your application.

3. Avoid Unnecessary Loops

Using loops in JavaScript can be expensive if you’re not careful. Cycling through a collection of items can put a lot of strain on the browser.

While you definitely can’t avoid loops in your code, you need to do as little work in them as possible. You can use other techniques that avoid the need to loop through the collection.

For example, you can store an array’s length in a different variable, rather than reading it during every iteration of the loop. If you get what you want from a loop, break out of it immediately.

4. Minify JavaScript Code

Image showing the css and javascript minifier

Minification is an effective method for optimizing JavaScript code. A minimizer transforms your raw source code into a smaller production file. They remove comments, trim unnecessary syntax, and shorten long variable names. They also remove unused code and optimize existing functions to take up fewer lines.

Examples of minimizers are Google Closure Compiler, UglifyJS, and Microsoft AJAX minifier. You can also manually minify your code by inspecting it and looking for ways to optimize it. For example, you can simplify the if statements in your code.

5. Compress Big Files With Gzip

Most clients use Gzip to compress and decompress big JavaScript files. When a browser requests a resource, the server can compress it to return a smaller file in the response. When the client receives the file, it decompresses it. Overall, this approach saves bandwidth and reduces latency, improving application performance.

6. Minimize DOM Access

HTML Document

Accessing the DOM can impact the performance of your application because the browser has to refresh with every DOM update. It’s best to limit DOM access to the least possible frequency. One way you can do this is by storing references to browser objects.

You can also use a library like React which makes changes to the virtual DOM before pushing them to the real DOM. As a result, the browser updates the parts of the application that needs updating, instead of refreshing the whole page.

7. Defer Unnecessary Load of JavaScript

While it’s essential that your page loads on time, not all functions need to be working on the initial load. Suppose you have a clickable button and a tab menu that reference JavaScript code; you can defer both until after the page loads.

This method frees up processing power, allowing you to render the necessary page elements on time. You delay compiling code that might hold the initial display of the page. Then, once the page finishes loading, you can start loading the functionalities. That way, the user can enjoy fast load time and begin interacting with the elements on time.

You can also include the smallest amount of CSS and JavaScript in your head element, so it loads immediately. Secondary code can then live in separate .css and .js files. This technique requires a decent knowledge of how the DOM works.

8. Use a CDN to Load JavaScript

Globe symbolizing the internet seen over a graphic illustration of a browser

Using a content delivery network helps to speed up page load time, but it’s not always effective. For example, if you choose a CDN without a local server in a visitor’s country, they won’t benefit.

To resolve this issue, you can use tools to compare several CDNs and decide which offers the best performance for your use case. To learn which CDN is best for your library, check out the cdnjs website.

9. Remove Memory Leaks

Memory leaks can negatively impact an application’s performance. Leaks occur when the loaded page takes up more and more memory.

An example of a memory leak is when your browser starts to slow down after a long session of working with the application.

You can use Chrome Developer Tools to detect memory leaks in your application. The tool records the timeline in the performance tab. Many memory leaks occur as a result of removing DOM elements. The garbage collector will only release memory once all variables referencing these elements are out of scope.

Chrome devtools show API timing

Tools like Lighthouse, Google PageSpeed Insights, and Chrome can help you detect problems. Lighthouse checks for accessibility, performance, and SEO issues. Google PageSpeed can help you optimize JavaScript to enhance your application’s performance.

The Chrome browser provides a Developer Tools feature which you can toggle by clicking F12 on your keyword. You can use its performance analysis to turn the network on and off and check CPU consumption. It also checks other metrics to uncover problems affecting your website.

As a web developer, you’re going to be working in your web browser a lot. Most browsers come with a suite of developer tools to help you with troubleshooting website issues. Google Chromes Developer Tools feature has many functions to assist you.