Front End Developer Interview Questions UK: 8 Real Questions and What Interviewers Want

Before your Front End Developer interview, it helps to see the questions from the interviewer's side. We have picked eight from our set of 25 and added the reason each one gets asked.

Eight Front End Developer interview questions, and what the interviewer is thinking

1. Can you explain closures in JavaScript and give a practical example of where you have used one?

Why they ask: Closures are one of the most frequent JavaScript questions and reveal real language understanding.

2. What is the difference between Flexbox and CSS Grid, and when would you use each?

Why they ask: Layout skills are central to front-end work and appear in nearly every interview.

3. How does the JavaScript event loop work, and why does it matter for front-end performance?

Why they ask: Understanding async behaviour is essential to avoid janky interfaces.

4. What do Core Web Vitals measure, and how would you improve them on a slow site?

Why they ask: Performance is now tied to SEO and conversion, and is a common practical topic.

5. What does a typical day as a front-end developer involve?

Why they ask: Checks you understand the real scope, including collaboration and quality work.

6. How do React hooks like useState, useEffect and useMemo work, and what mistakes do people commonly make with them?

Why they ask: If the role uses React, this is almost guaranteed.

7. A page works in Chrome but looks broken in Safari on iPhone. How do you debug it?

Why they ask: Cross-browser debugging is a regular real-life scenario.

8. Tell me about a time you significantly improved the performance of a website or web application.

Why they ask: A strong competency question with clear measurable outcomes.

A sample answer to question 1

Can you explain closures in JavaScript and give a practical example of where you have used one?

A closure is a function that remembers the variables from the scope where it was created, even after that outer function has finished running. Because of that, the inner function keeps access to those variables. A practical example is a debounce utility for a search box: the outer function holds a timer variable, and the returned function clears and resets that timer each time the user types. The timer survives between calls precisely because of the closure. Closures are also how React hooks such as useState and useEffect capture values, which is why you sometimes get stale closures, for example an effect reading an old value because its dependency array is wrong. They're useful for private state and factory functions, but I'm mindful that holding references to large objects can cause memory leaks if listeners are never removed.

Common mistake to avoid: Giving only a definition; Not mentioning hooks pitfalls

Want the rest?

Full model answers, key points and common mistakes for all 25 questions are on the Front End Developer interview questions page. The first five are free, no sign-up needed.