Frontend vs Backend Bottlenecks in Real Web Apps

Performance and speed are major challenges in modern digital products. You're probably familiar with the frustration of clicking a button and seeing a spinning loader that never stops. Frontend vs backend performance is a perennial discussion when it comes to product development and improvement for a digital product. This article covers the unique performance issues of each layer and offers practical tips and tricks for frontend backend optimization performance to deliver a top-notch user experience.

Frontend vs Backend in Web Development

The first thing we need to do to diagnose performance problems is to separate the two legs of building the web.

The frontend is known as the "client-side", and it is all that the user sees and interacts with. This includes the layout, buttons, images and the logic that executes inside the browser. The backend or "server side", on the other hand, is like the engine under the hood. It does all the work of data storage, security and complex business logic that drives the interface.

When a user accesses a page, the backend handles the request and returns the appropriate files. The frontend then pulls those files and paints the corresponding pixels on the screen. Web app performance bottlenecks are a major concern for full-stack developers, as a performance blockage at either point can lead to a poor user experience.

Common Frontend vs Backend Bottlenecks

The initial usability metric for a web page is its interactivity time. No matter how fast your server is, a bloated frontend can make the application feel sluggish. 

Common Frontend Performance Bottlenecks

We primarily measure frontend performance by how quickly a page becomes interactive. Even if your server is lightning-fast, a bloated frontend can make the application feel sluggish.

Heavy JavaScript Files

JavaScript frameworks are of paramount importance in modern web apps. In some cases, sending a lot of scripts to the browser can cause "main thread blocking". The browser locks up when it runs complex code, so it can't respond to any user actions, like clicks or scrolling.

Unoptimized Images and Media Files

Images with high resolution that aren't compressed result in slow loading times. If a browser needs to download 5MB of images before it is usable, then the user will bounce. With the use of modern formats and responsive image techniques, it is very important for front-end optimization and back-end optimization.

Render-Blocking CSS and JavaScript

If you have a CSS or JS file in the header, then a browser will not render the rest of the page until it is downloaded. This can delay page rendering and negatively impact user experience. 

Cumulative Layout Shift (CLS)

Although not a "speed" problem, layout shifts are shifts in the position of elements as the page loads. This issue occurs when the dimensions of the image are not specified, and the browser calculates the layout more than once, thereby using up client resources.

Common Backend Performance Bottlenecks

The true job is done at the back end. Frontend optimizations alone cannot fully resolve inefficient server-side logic. 

Slow Database Queries

This issue is likely the most frequent of performance-related web app bottlenecks. A poorly formed query (e.g., retrieving thousands of rows instead of five) slows down the response time from the database, which in turn slows down the query/response process.

No Caching System

When the server has to do the same calculation or database query for each user, it will stall and/or crash during heavy load. Without a caching layer, the backend has to do more than its fair share of work.

Slow Third-Party APIs

Most apps today use external services for payments, maps, authentication and more. When the third-party API takes time to respond, and the backend app is waiting for that response before passing it on to the frontend, your app's performance becomes dependent on another company's infrastructure.

Poor Server Configuration

Sometimes the problem is not the code -- it's the environment. The backend may become overloaded during peak hours because of low RAM, CPU cycles, or the absence of load balancing.

How to Improve Frontend and Backend Bottlenecks

Addressing performance problems in web apps is a two-part process: frontend and backend. 

Fixing Frontend Bottlenecks

After determining that the issue is with the browser, some optimisation techniques for the frontend-backend can be implemented to improve the user experience on the client side.

Use Code Splitting

Split the code of the application into multiple JavaScript files rather than loading all of them at once. This enables the browser to download only the code necessary for the page he/she is reading. For most modern builders, this process is automatic once they are configured properly.

Optimize Images and Use CDNs

• Compression: Reduce the size of an image without losing quality, especially using tools.

• Modern Formats: Switch from PNG/JPG to WebP or AVIF, a more efficient format.

• Lazy Loading: only load images when they are in the view window.

• CDNs: Cache the static files in a content delivery network. CDNs deliver static files from servers located closer to users, helping reduce latency and improve loading speed. 

Minify CSS and JavaScript

Clean up all your CSS and JS files, removing all unnecessary characters (whitespace and comments). Also, make sure that your server compresses files even more before sending them over the network with compression, Gzip or Brotli.

Fixing Backend Bottlenecks

On the back-end side, resolving problems means making the server work smarter – not harder.

Optimize Database Queries

An index is similar to a table of contents in your database. When you index columns that you commonly use in queries, Proper indexing can significantly reduce query execution time and improve database performance. Also, don't use 'SELECT *' queries—only get the data points your front end really needs.

Adding Caching Layers

What is the need to calculate the same data again and again? Cache the result of costly database queries, such as caching systems. Then, the next time a user requests that data, the server will be able to serve it up instantly from memory, without having to hit the database.

Use Background Job Processing

If you have a heavy procedure, such as processing payments or reporting, then run it in the background. The backend should respond immediately, saying that the report has been started ("We've started your report!"), and the user can go on using the app while the report works in the background.

Frontend vs Backend Comparison

The table below highlights the key differences between frontend and backend performance bottlenecks in web applications: