Techniques for Enhancing JavaScript Performance

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Techniques for Enhancing JavaScript Performance

Javascript Nov 12, 2022

Every experienced developer understands how critical and time-consuming it is to maintain application performance. When it comes to loading, seconds might be the difference between a successful business and a disaster. As a result, the developer is in charge of ensuring that the programme delivers a better user experience, improved conversion rates, and, ultimately, happier consumers.

>16 milliseconds Threshold

The event loop is used by JavaScript to complete tasks. The concept is straightforward: an endless loop waits for a job, performs it, and then returns to the waiting state until a new task comes.

The event loop's work is divided into discrete jobs (such as running a loaded script or moving the mouse), microtasks, and rendering modifications, which we'll go through briefly below. While another job is underway, rendering does not take place. As a result, for a comprehensive user experience, everything in the event loop must occur in a timely way.

Device parameters, such as screen refresh rate, power saving mode, or browser settings, have the most impact on rendering time. While browsers strive to provide content to users as soon as possible, most current displays support a refresh rate of 60 frames per second. This provides us with only 16 milliseconds to perform the work at hand without disappointing the user with frame dropouts.

Most JavaScript activities are easy enough to finish in such a short period of time. However, as current online applications get more complicated, the client-side becomes an extravaganza with an abundance of features and computations that exceed our 16 millisecond barrier
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Processing Large Amounts of Data

Computing a huge quantity of data can soon surpass all kinds of restrictions and cause the event loop to become stalled. Particularly if we try to perform everything on a single thread. In this instance, the browser will be unable to display anything until our data has been processed. As you may expect, this does not deliver the best user experience.


SetTimeout allows you to divide calculations into smaller chunks.

Utilizing web workers is the second choice. They allow the browser to display the picture as quickly as possible by running scripts in the background so they don't interfere with activities on the main thread.

Excessive reliance on external libraries

Even the most well-liked third-party libraries do not always support optimization. Consider bcrypt, which hashes a text using 13 rounds. Each cycle lasts for around two seconds, which delays the main thread and prevents other connections from operating.

Although this doesn't effect rendering directly and only takes 16 milliseconds, encryption is a good illustration of how poorly designed libraries may negatively impact your application.


Optimized libraries are the best option in this case. Look for libraries created especially for Node.js, as they make advantage of C++ bindings that let you parallelize threads and carry out computations up to three times more quickly.


This is a common performance problem, especially for SPA apps that dynamically add and delete content. Your browser determines where each page element should be rendered, as well as its size and relationship to other objects, during the layout phase of the rendering queue.

Unsurprisingly, the procedure takes longer the more DOM objects there are on the page. The most challenging aspect is that even the slightest style modification would invalidate earlier computations and initiate a brand-new Layout process.


The activities of measuring (reading) and modifying (writing) element styles must be organised extremely carefully. To avoid making layout restart several times, I advise grouping these operations. This could take a while on a big job, but you'll be amazed at how helpful it can be.

Large builds

Large scripts are huge issues. The longest page load time is caused by the execution of JavaScript files. As opposed to producing a picture, which is simply a group of pixels on the screen, this process can take significantly longer since it involves parsing, script execution, scope creation, and other processes.

As a result, optimising JavaScript files is crucial to enhancing your application's speed. To determine the size and content of the generated files, use the Webpack Bundle Analyzer.


Solution 1: Lazy loading is the ideal approach for React. Instead of adding all the code in one file, React.lazy will let you utilise dynamic imports, which are capable of dividing your code into smaller chunks.

Solution 2: If shrinking the files' size isn't an option, think about caching them so that the programme won't have to refresh them each time. There are 4 headers for files that are cached:

  • ETag - A unique code that enables the web server to avoid transmitting the entire response whenever the content has not changed;
  • Cache-Control - Includes guidelines you may use to manage your cache - shows the cache lifetime;
  • Expires - shows the cache lifetime;
  • Last-Modified - Contains the last modification time and date of the file.

Solution 3: The Brotli compression standard should be used instead of Gzip since it is more effective, even though both are supported by the majority of browsers.

Increasing JavaScript speed is essential for effective UI performance. I simply briefly discussed a few significant issues that you could run into in this article. Thanks!


Anurag Deep

Logical by Mind, Creative by Heart