Targeted practice
Work on exactly the concept you need—without boilerplate.
Frontend interview training
Train for the interview.
Show up ready.
Practice the JavaScript, React, and UI problems frontend candidates actually face—with instant tests and senior solutions.
Longest Substring 8 tests passedJavaScript⌄
1
export function longestSubstring(input) {2 let left = 03 let longest = 04 const seen = new Map()5 6 for (let right = 0; right < input.length; right++) {7 const char = input[right]8 if (seen.has(char)) left = seen.get(char) + 19 seen.set(char, right)10 longest = Math.max(longest, right - left + 1)11 }12 return longestTestsSolution
✓8 / 8 tests passed
- ✓handles empty input2 ms
- ✓handles a single character1 ms
- ✓handles repeated characters1 ms
- ✓handles mixed characters2 ms
- ✓handles unicode characters1 ms
- ✓handles special characters1 ms
2,500+engineers
120+questions
600+tests
Built by engineers. Trusted by developers at top companies.
The old way
Stop assembling your own curriculum
Frontend prep should not feel scattered.
Hours of videos, articles, and disconnected prompts still leave you wondering whether your solution handles the edge cases an interviewer cares about.
Clientside gives youthe prompt, the workspace, the tests, and the explanation.
Built for frontend developers
Turn practice time into visible progress.
01
Interactive from the first keystroke.
Skip setup and work inside a browser-based playground with starter code, previews, and everything the exercise requires.
02
Feedback that closes the loop.
Run real test suites, catch edge cases immediately, and compare your approach with a senior-written solution and walkthrough.
Real questions
Prepare with prompts sourced from actual frontend interviews.
Senior solutions
Understand the reasoning, tradeoffs, and final implementation.
Engineer approved
Practice that feels like the real thing.
Build confidence with focused work, immediate feedback, and explanations that make the solution stick.
“
Solving Leetcode puzzles might be great for learning algorithms, but it will not prepare you for frontend interviews or teach you React internals. Clientside is an incredible solution that I recommend whenever someone mentions practicing frontend.
Rory M.Software Engineer at QueryLayer“
The exercises are interactive and come straight from real interviews, so it feels like you are getting a real taste of what to expect. It also helped me find knowledge gaps I did not know I had.
Mucahit Y.Software Engineer at HubSpot“
Clientside is amazing. The problems are engaging, challenging, and reflective of actual frontend technical interviews. It has become a regular study tool for me.
Zile C.Engineer at Weavechain“
I have worked as a frontend developer for two years, yet I still find some of the easy questions challenging. I highly recommend Clientside to anyone interested in practical coding challenges.
Albert C.Frontend EngineerWhat you will practice
Your frontend interview curriculum.
React Hooks
Build advanced and reusable hooks.
→User Interfaces
Match UI specifications with JavaScript and React.
→Data Structures
Transform data with modern JavaScript methods.
→JS Fundamentals
Strengthen the concepts interviews depend on.
→Full Interviews
Practice realistic prompts with immediate feedback.
→Leveled Challenges
Progress from fundamentals to harder edge cases.
→Top Questions
Study questions asked by leading companies.
→Test Suites
Check every solution against real requirements.
→One price. No puzzle.
Access the complete frontend training platform.
Practice the questions you can expect in interviews and on the job.
Clientside Pro
Lifetime access
Everything you need to prepare with intention and keep sharpening your frontend skills.
$39one time
Upgrade to Pro Try the exercises firstIncluded with Pro
- 120+ interview questions
- 600+ unit tests
- Senior-written solutions
- Questions from real interviews
- New exercises added regularly
- All future platform updates
Your next interview starts here
Practice with purpose.
Start free. No setup and no credit card required.