How to Build Complex User Interfaces Without Going Completely Insane

Building modern web user interfaces is hard. As front-ends grow in size and complexity, it becomes increasingly challenging to manage the intricacies of state, performance, consistency and accessibility. Without the right tools and approaches, even a small UI can quickly become an unwieldy tangle of components and edge cases.

Consider these statistics:

• The average webpage is now 2MB in size, with nearly 70% of that coming from JavaScript code (source)
• A typical web app now has over 1000 UI components (source)
• Poor accessibility costs businesses up to $6.9 billion annually (source)

As a long-time front-end architect, I‘ve experienced first-hand how unruly UI codebases can hamper development velocity and lead to bugs and inconsistencies. However, I‘ve also discovered principles and techniques that can keep even the most complex front-ends manageable. Here are some of the key lessons I‘ve learned.

Embrace Modularity

Perhaps the most important principle for building maintainable UIs is modularity. Just as we break server-side code into focused modules and microservices, the front-end should be composed of small, single-purpose components.

"The key to building large apps is never build large apps. Break your applications into small pieces. Then, assemble those testable, bite-sized pieces into your big application" – Justin Meyer, author JavaScript MVC

With modern component-based frameworks like React, Angular and Vue, it‘s easier than ever to build UIs in a modular fashion. By encapsulating markup, styles and behaviors into reusable components, you can enforce separation of concerns and keep the codebase DRY.

For example, consider the components that make up a typical e-commerce product page:

(source)

Rather than a single monolithic page, the UI is composed of several modular components like ProductImage, ProductDetails, and AddToCartButton. Each component is responsible for a specific aspect of the page and can be developed and tested in isolation.

This modular architecture has several key benefits:

• Easier to reason about and maintain each component
• Components can be reused across pages and projects
• Clearer separation of concerns
• Components can be updated without unintended side-effects
• Multiple developers can work on separate components simultaneously

Of course, components alone aren‘t enough. You also need a way to share state and behaviors between them. Libraries like Redux and MobX provide patterns for managing application-level state outside of the UI components themselves. This keeps your component code lean and focused.

Leverage Existing Solutions

As the old adage goes, "good developers copy, great developers steal". When it comes to building complex front-end interfaces, there‘s no need to reinvent the wheel. Whenever possible, leverage existing frameworks, libraries and tools to solve common problems.

Take component frameworks like Material UI and Ant Design. These robust UI libraries provide pre-built, fully-tested components for everything from buttons and form fields to data tables and drawers. Using them as a foundation can dramatically speed up development compared to building everything from scratch.

These frameworks also encapsulate UX best practices and ensure consistency across your UI. Studies have shown that a consistent UI can increase user efficiency by up to 35% (source).

That‘s not to say you should use a component framework for everything. In cases where you need highly bespoke UI or have unique performance requirements, it may still make sense to build custom components. The key is striking the right balance and not being afraid to stand on the shoulders of giants when it makes sense.

Prioritize Testing

No matter how well-architected your UI is, bugs are inevitable, especially as complexity grows. That‘s why automated testing should be a first-class citizen in any front-end codebase.

I‘m a big proponent of the testing pyramid, which suggests you should have many small unit tests, fewer integration tests, and even fewer end-to-end tests. For UI development, I‘ve found the following mix to be effective:

• Unit tests for individual components and functions
• Snapshot tests for catching unintended changes in component markup and styles
• Integration tests for key user flows
• A small number of end-to-end tests that exercise the entire app

Modern testing frameworks like Jest, Mocha and Cypress make it easy to automate tests for various aspects of the UI. I‘m particularly fond of snapshot testing for UI components. Essentially, you render a component, take a "snapshot" of the markup, and compare future versions against this saved snapshot. If the markup changes unexpectedly, the test fails, alerting you to a potential regression.

"Snapshot testing has been an absolute game-changer for us. It‘s caught countless regressions that would have otherwise slipped through the cracks." – Sunil Pai, Engineering at Coinbase

Another technique I recommend is headless browser testing. Tools like Puppeteer and Cypress let you programmatically control a browser and simulate user actions like clicking and typing. Unlike unit tests which test code in isolation, these end-to-end tests verify that the entire UI works together as expected.

Keep in mind, the goal isn‘t to test every possible edge case or strive for 100% code coverage. Rather, focus your testing efforts on the most critical paths a user can take through your app. And whenever a new bug is discovered, add a test to prevent it from recurring.

Accessibility Matters

Accessibility is one of the most overlooked aspects of UI development. Many teams treat it as an afterthought or nice-to-have. However, neglecting accessibility doesn‘t just exclude a significant portion of your potential users, it makes for a worse overall user experience.

Consider that almost 13% of the US population has some form of visual disability (source). If your UI doesn‘t accommodate screen readers, high-contrast modes, and keyboard navigation, you‘re putting unnecessary barriers in front of these users.

The good news is that building accessible interfaces is relatively straightforward. The Web Content Accessibility Guidelines (WCAG) outline four key principles:

1. Perceivable – Information and UI components must be presentable to users in ways they can perceive (e.g. alt text for images)
2. Operable – UI components and navigation must be operable (e.g. keyboard-accessible)
3. Understandable – Information and UI operation must be understandable
4. Robust – Content must be robust enough to be interpreted by a wide variety of user agents, including assistive technologies

There are a number of tools that can help automate accessibility testing. Lighthouse is a popular one that generates an accessibility score along with specific recommendations for improvement. I recommend running Lighthouse in your CI pipeline and failing the build if the score drops below 90%.

Invest in Developer Experience

When building complex UIs, it‘s easy to focus solely on the end-user experience. However, don‘t forget about the developers who have to build and maintain the front-end. The easier you make it for new team members to get up-to-speed and contribute, the faster you‘ll be able to iterate and ship new features.

Documentation is key here. At minimum, I recommend maintaining a high-level architectural overview, a component library with examples, and a style guide. Tools like Storybook, Docz and React Styleguidist can generate component documentation from your codebase.

Another area to focus on is the developer environment. With modern front-end tooling, it‘s not uncommon for a new developer to have to run a gauntlet of installers, dependency managers and build tools just to get the UI running locally. Investing in a dockerized environment that runs with a single command can eliminate a lot of this friction.

Ultimately, the goal should be to make working with the UI codebase as frictionless as possible. Every minute a developer spends wrestling with tooling or deciphering cryptic code is a minute not spent delivering value to end users.

Continuously Monitor and Optimize

Finally, building a complex UI doesn‘t end when you deploy to production. To deliver the best possible experience to users, you need to continuously monitor UI performance and iterate based on real-world usage data.

At a minimum, you should be tracking:

• Page load times
• Interaction responsiveness (e.g. time to first input)
• JavaScript bundle sizes
• Error rates

Tools like Sentry, TrackJS and LogRocket can provide detailed insights into front-end performance and help you quickly identify and fix issues. I also recommend using analytics to understand how users are actually interacting with the UI. Tracking metrics like feature adoption, user flows and drop-off points can highlight areas for optimization.

Another key aspect of monitoring is accessibility. Tools like axe and WAVE can continuously scan your UI and alert you to accessibility issues. I‘ve found it useful to integrate these into the development process so accessibility problems are surfaced early.

The landscape of devices and browsers accessing your UI is constantly evolving. What works well today may not hold up a year from now. Investing in continuous monitoring and improvement allows you to adapt to changing requirements and deliver the best possible experience to your users.

Conclusion

Building complex, performant and accessible user interfaces is hard. As front-ends continue to grow in scope and sophistication, it can feel like an uphill battle keeping everything running smoothly. However, by following the principles and techniques outlined in this post, you can tame even the most unruly interfaces.

To recap, the key strategies for building complex UIs are:

1. Embrace modularity
2. Leverage existing solutions
3. Prioritize testing
4. Make accessibility a requirement
5. Invest in developer experience
6. Continuously monitor and optimize

Of course, this is just the tip of the iceberg. The world of front-end development is constantly evolving with new frameworks, libraries and best practices. The most important thing is to stay curious and never stop learning.

At the end of the day, building great user interfaces is both an art and a science. It requires a deep understanding of your users, a passion for sweating the details, and constant iteration. But when you get it right, it‘s one of the most rewarding feelings in software development. So embrace the complexity, keep pushing forward, and remember: you‘ve got this!