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12,593 front end developer intern interview questions shared by candidates

1. If I start a startup would I prefer writing unstructured code in two month or clean, efficient, testable code in a year. (Comparing 2 vs 12 months is a totally unrealistic example. Experienced developer would add new features faster when she/he has clean and well designed code base. There will be fewer bugs also. A good code base would never take 6 times longer to develop.) 2. Would I spend time to add a feature to Web app or to migrate it to ES6? 3. Why do some of TransferWise users drop off at the fourth transfer flow process, which is entering billing information? 4. What would I change to make more users to enter their billing information? 5. How would I know that my change improved the statistics if there were 10 more changes?
avatar

Front-end Web Developer

Interviewed at Wise

3.7★
Sep 14, 2015

1. If I start a startup would I prefer writing unstructured code in two month or clean, efficient, testable code in a year. (Comparing 2 vs 12 months is a totally unrealistic example. Experienced developer would add new features faster when she/he has clean and well designed code base. There will be fewer bugs also. A good code base would never take 6 times longer to develop.) 2. Would I spend time to add a feature to Web app or to migrate it to ES6? 3. Why do some of TransferWise users drop off at the fourth transfer flow process, which is entering billing information? 4. What would I change to make more users to enter their billing information? 5. How would I know that my change improved the statistics if there were 10 more changes?

Serialise IDs from a nested tree of items
 const data = [
  { id: 1, items: [{ id: 4, items: [{id: 5}, {id: 6, items: [{id: 8}]}]}]},
  { id: 2, items: [{ id: 7}]},
  { id: 3 },
  { id: 9, items: [{id: 10, items: [{id: 12}]}, {id: 11}] }
];

// Should return [1, 2, 3, 9, 4, 7, 10, 11, 5, 6, 12, 8] 
avatar

Senior Front End Developer

Interviewed at Apple

4.2★
Nov 10, 2017

Serialise IDs from a nested tree of items
 const data = [
  { id: 1, items: [{ id: 4, items: [{id: 5}, {id: 6, items: [{id: 8}]}]}]},
  { id: 2, items: [{ id: 7}]},
  { id: 3 },
  { id: 9, items: [{id: 10, items: [{id: 12}]}, {id: 11}] }
];

// Should return [1, 2, 3, 9, 4, 7, 10, 11, 5, 6, 12, 8] 

They asked me to explain how I would approach optimizing the performance of a web application. It was a great question because it allowed me to demonstrate my practical experience, talk about specific tools and techniques I use, and show how I think through real-world challenges.
avatar

Senior Front End Developer

Interviewed at EPAM Systems

4★
Apr 18, 2025

They asked me to explain how I would approach optimizing the performance of a web application. It was a great question because it allowed me to demonstrate my practical experience, talk about specific tools and techniques I use, and show how I think through real-world challenges.

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