What Are The 10 Most Common JavaScript Performance Issues, And How Can They Be Resolved?
Performance is one of the most crucial considerations when developing a website or an application. Nobody wants a webpage to load slowly or an app to break, and users should not have to wait for too long. Forty percent of visitors will abandon a website if it takes more than three seconds to load, and forty-seven percent of visitors expect a website to load in less than two seconds, according to Kissmetrics.
In this guide, you will find the top 10 most common javascript performance issues and its methods with easiest ways.
Performance ought to be constantly considered while developing your web apps with these figures in mind. Here are some strategies to successfully enhance application speed to get you started:
What are the key topics you will learn from the JavaScript syllabus?
The 10 Most Common JavaScript Issues Developers Face In 2025
1. Browser cache
There are two ways to accomplish this. The first is to deploy a service worker in order to leverage the JavaScript Cache API. Using the HTTP protocol cache is the second option.
To access a particular item, scripts are frequently utilized. Performance may be instantly improved by putting a repeated access object within a user-defined variable and utilizing that variable in subsequent accesses to that item.
2. Specify the context of execution
You must create a set of clearly defined settings where you can test the code’s performance in order to quantify any changes you’re making to your application.
It is not practical to try to do optimizations and performance testing for every Javascript engine version. However, testing in a single setting is not a smart approach since it may yield incomplete data. Therefore, it’s critical to create many distinct contexts and make sure the code functions well in each.
3. Get rid of any extra JavaScript
This step will shorten the time it takes for the browser to examine and build the code in addition to the transmission time. You need to consider the following factors in order to achieve this:
It’s a good idea to eliminate any feature that people aren’t using along with all of the JavaScript code that goes with it. This will improve user experience and speed up website loading.
Another possibility is that you have dependencies that provide some feature that is already naturally available in all browsers without requiring the usage of extra code, or that a library was accidentally included and is not required.
Read Also: What are the top 10 JavaScript concepts programmers should know to excel in web development?
4. Steer clear of excessive memory use
Since it is impossible to determine how much memory the device using your app needs, you should always aim to utilize as little RAM as feasible. JavaScript is suspended and the browser’s garbage collector is run whenever your code asks the browser to reserve more memory. The page will function slowly if this occurs often.
5. Postpone the unnecessary JavaScript load
Although users expect a website to load quickly, not all features probably need to be accessible when the page first loads. It is possible to postpone loading a function until after the first page load if the user has to take a certain action (such as clicking on an element or switching tabs) in order for the function to be run.
You can avoid loading and compiling JavaScript code in this method, which would cause the website to show more slowly at first. We may begin loading those features as soon as the page loads completely, making them accessible as soon as the user begins interacting. Google advises using 50ms blocks for this deferred load in the RAIL model to avoid interfering with the user’s interaction with the website.
6. Prevent memory leaks
A persistent memory leak will cause the loaded page to reserve more and more memory, eventually filling the device’s available memory and negatively affecting performance. This kind of failure is undoubtedly something you’ve seen (and possibly been annoyed about), usually on a page that has an image slider or carousel.
By creating a timeline in the Performance tab of Chrome Dev Tools, you can determine whether your website has memory leaks. Memory leaks are typically caused by DOM elements that are deleted from the page but have a variable referencing them, making it impossible for the garbage collector to remove them.
7. When you need to run code that requires a lot of execution time, use web workers.
The Mozilla Developers Network (MDN) documentation states that Web Workers enables the execution of script operations on a background thread that is distinct from the web application’s main execution thread. The benefit of this is that time-consuming operations may be carried out on a different thread, freeing up the main thread — typically the user interface — from blocking or slowing down.
Without interfering with the user interface thread, web workers enable your code to execute computations that need a lot of processing power. For optimal efficiency, web workers let you create new threads and assign tasks to them. In this manner, the main thread may continue to function without being blocked by long-running processes that would often block other jobs.
8. Save a DOM item in a local variable if you access it several times.
The DOM is slow to access. It is preferable to store an element’s content in a local variable if you plan to read it several times. However, it’s crucial to remember that the variable should be set to “null” if you want to delete the DOM’s value later to prevent memory leaks.
9. Give local variable access first priority.
After determining if a variable exists locally, JavaScript gradually expands its scope to include global variables. JavaScript can access variables considerably more quickly when they are saved in a local scope.
Local variables can traverse through several layers of scope and are located according to the most specific scope; the lookups may provide general searches. It’s crucial to use let or const before each variable when defining the function scope within a local variable without a prior variable declaration. This will help to speed up the code and avoid lookups.
10. Steer clear of global variables
When referring global variables from within a function or another scope, the scripting engine must search through the scope; hence, if the local scope is lost, the variable will be deleted. Performance will be enhanced if variables in the global scope are unable to endure during the script’s lifespan.
