Crack Frontend Interviews
Practice 500+ real questions across UI coding, JavaScript, and system design, with a detailed solution for every one.
User Interface
Explore questionsEvery question comes with a working solution, a step-by-step explanation, interviewer grading criteria, and time checkpoints. Write React or vanilla JavaScript and see the result instantly.
System Design
Explore system designEvery question is broken down with the same step-by-step framework, from requirements to a complete architecture. Then go deeper: monorepos, microfrontends, real-time transports, future-proof components.
JavaScript Coding
Every question has a working solution and a step-by-step explanation. Run your code in the browser and check it against the solution.
Practice JavaScriptfunction debounce(fn, wait) {
let timer;
return (...args) => {
clearTimeout(timer);
timer = setTimeout(fn, wait, ...args);
};
}
const save = debounce(write, 300);
save(); save(); save();Conceptual
Explore conceptualEvery question gives you a short answer to say in the interview and the reason interviewers ask it. Event loop, closures, rendering, networking.
Explain the event loop
tap to flip · drag for the next cardThe event loop lets JavaScript handle non-blocking work on a single thread. It keeps checking the call stack, and whenever the stack is empty it picks the next task from the queues and pushes it on for execution.
read the full answerWhat is a closure?
tap to flip · drag for the next cardA closure is a function that remembers the variables of the function it was created in, even after that outer function has returned. It works because every function keeps a reference to the scope it was defined in.
read the full answerWhat happens when you type a URL?
tap to flip · drag for the next cardThe browser resolves the domain through DNS, opens a TCP and TLS connection, and sends an HTTP request. The server responds with HTML, and the browser parses it, fetches linked resources, and renders the page.
read the full answerHow does CORS work?
tap to flip · drag for the next cardCORS is how a server tells the browser which other origins may read its responses. Cross-origin reads are blocked by default and only allowed when the server opts in with Access-Control headers, sometimes after a preflight request.
read the full answerPractice in a real editor.
Monaco, live tests, and console output. No local setup.
Questions
500+ practice questions across UI, JS, and concepts.
System design
Question breakdowns and system design core concepts for senior roles.
Solutions
Expert solutions with best practices for every question.
Test cases
Evaluate your code against real test cases.
Evaluation
Interviewer evaluation criteria from top companies.