Javascript is vital to web development. Language is behind most of the interactivity and animation you’ll see on websites. But JavaScript can also slow down a website if the code is poorly written. Inefficiencies can result in both poor loading times and slow rendering speeds.
Adopt the following best practices to improve the speed and performance of your website.
1. Define variables locally
Apply Online:
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. Scopes only reside within the function in which they are declared. Global variables are variables that can be accessed throughout the script. In case of global variables, the scope persists throughout the program.
Whenever you try to access a variable, the browser does something known as a scope lookup. It checks the scope closest to the variable and keeps looking until it finds the variable. Thus, the higher the scope chain in your program, the longer it will take to access variables beyond the current scope.
For this reason, it is always best to define your variables close to the execution context. Use global variables only on rare occasions; When you want to store data used throughout the script, eg. This will reduce the number of workspaces in your program, which will improve performance.
2. Load JavaScript Asynchronously
JavaScript is a single-threaded programming language. This means that once a function is executed, it has to run till the end before any other function can run. This architecture can lead to situations in which code can block threads and freeze the app.
In order for threads to perform well, you should run some time-wasting tasks asynchronously. When a task runs asynchronously, it does not take up all the processing power of the thread. Instead, the function joins an event queue where it is fired after all other code has executed.
API calls are perfect for asynchronous patterns because they take time to resolve. So instead of letting it hold a thread, you would use a promise-based library like the Fetch API to fetch the data asynchronously. This way, the browser can run other code while retrieving data from the API.
Understand the intricacies of asynchronous programming and you will improve the performance of your applications.
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 certainly 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 the length of an array in a different variable instead of reading it during each iteration of the loop. If you get what you want from a loop, break it out immediately.
4. Minify JavaScript Code
Minification is an effective way to optimize JavaScript code. A minimizer turns your raw source code into a small 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 the Google Closure Compiler, UglifyJS, and the Microsoft AJAX Minifier. You can narrow it down manually by inspecting your code and looking for ways to optimize it. For example, you can simplify the if statements in your code.
5. Compress Large Files with Gzip
Most customers use Gzip to compress and decompress large JavaScript files. When a browser requests a resource, the server can compress it to return a smaller file in response. When the client receives the file, it decompresses it. Overall, this approach saves bandwidth and reduces latency, thereby improving application performance.
6. Minimize DOM Access
Accessing the DOM can impact the performance of your application as the browser has to be refreshed with every DOM update. It’s best to limit DOM access to the lowest possible frequency. One way to do this is by storing references to browser objects.
You can also use a library like React which commits changes to the virtual DOM before pushing to the real DOM. As a result, the browser updates the parts of the application that need to be updated instead of refreshing the entire page.
7. Avoid unnecessary load of JavaScript
While it is important that your page loads on time, it is not necessary that all functions work on the initial load.