Preparing for JavaScript technical interviews requires practicing problems across core data structures and asynchronous runtime mechanics. Here is a curated collection of essential coding interview problems categorized by topic.
Array & Hash Map Problems
1. Two Sum
- Difficulty: Easy
- Tests: Hash map lookup, O(N) time complexity optimization.
- Description: Given an array of integers
nums and a target integer target, return indices of the two numbers such that they add up to target.
- *Practice Two Sum on Pairlet.*2. Three Sum
- Difficulty: Medium
- Tests: Two-pointer techniques, sorting, deduplication.
- Description: Find all unique triplets in an array that sum up to zero.
- *Practice Three Sum on Pairlet.*
3. Group By Utility
- Difficulty: Easy / Medium
- Tests: Array reduction, higher-order functions, object key grouping.
- *Practice Group By on Pairlet.*
String & Stack Problems
4. Valid Parentheses
- Difficulty: Easy
- Tests: Stack data structures, bracket balance validation.
- Description: Determine if a string containing bracket characters
(), {}, [] is valid and properly ordered.
- *Practice Valid Parentheses on Pairlet.*5. Longest Substring Without Repeating Characters
- Difficulty: Medium
- Tests: Sliding window technique, Set / Map tracking.
- *Practice Longest Substring Without Repeating Characters on Pairlet.*
Async & Control Flow Problems
6. Implement Debounce
- Difficulty: Easy / Medium
- Tests: Closures, timer management (
setTimeout, clearTimeout).
- *Practice Implement Debounce on Pairlet.*7. Implement Throttle
- Difficulty: Medium
- Tests: Timestamp tracking, rate limiting.
- *Practice Implement Throttle on Pairlet.*
8. Implement Promise.all
- Difficulty: Medium
- Tests: Promise constructor, asynchronous coordination.
- *Practice Implement Promise.all on Pairlet.*
9. Concurrency Limiter
- Difficulty: Hard
- Tests: Queue management, promise batching.
- *Practice Concurrency Limiter on Pairlet.*
Code Review Problems
10. N+1 Query Fix
- Difficulty: Medium
- Tests: Identifying database N+1 performance anti-patterns.
- *Practice N+1 Queries on Pairlet.*
Practice Coding Problems Live
Try any of these problems live in a collaborative interview room with candidates. Explore All Pairlet Problems.
Frequently Asked Questions
What categories of coding problems should I prepare for JavaScript roles?
Focus on Array & Hash Map manipulation, String parsing, Stack matching, Async Promises/Control Flow, and Code Review bug detection.
Practice Relevant Coding Problems
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