ThoughtSpot Frontend SE Interview Experience
Overview
This document details a frontend software engineer interview experience at ThoughtSpot. The process evaluated the candidate's proficiency in JavaScript fundamentals, React development, and asynchronous programming. The role was for a Software Engineer (Frontend) position with a compensation range of 40-60 LPA. The application was submitted via Instahyre.
Interview Rounds
The interview process consisted of three rounds, each focusing on different aspects of frontend engineering.
Round 1: JavaScript Fundamentals & Code Snippets
This round assessed the candidate's understanding of core JavaScript concepts and performance optimization techniques. The evaluation included both theoretical questions and code snippet challenges.
- JavaScript Theoretical Questions: The interviewer posed questions on the following topics:
- Closures & Lexical Scope: Understanding of closure mechanics and practical applications.
- Event Loop & Microtasks vs. Macrotasks: Knowledge of asynchronous operation handling in JavaScript.
- Prototype & Prototypal Inheritance: Differentiation between
__proto__andprototype.
- Code Snippet Challenge: The candidate was required to predict the output of a given JavaScript code snippet and explain its behavior.
- Implementing a groupBy Polyfill: The candidate was tasked with implementing a
groupByfunction, similar to the Lodash implementation. Performance considerations and edge cases were also discussed. The following code was presented as a reference:
const groupBy = (array, key) => {
return array.reduce((result, item) => {
const groupKey = item[key];
if (!result[groupKey]) {
result[groupKey] = [];
}
result[groupKey].push(item);
return result;
}, {});
};
- Web Performance Optimization: A discussion covering frontend performance optimization strategies, including:
- Lazy Loading & Code Splitting
- Debouncing & Throttling
- Critical Rendering Path Optimization
- Browser Caching Strategies
The candidate successfully cleared this round.
Round 2: React Coding Challenge
This round involved building a real-world feature using React. The candidate was required to implement a typeahead search functionality.
-
Implementing a Typeahead Feature: The candidate was asked to build a typeahead (auto-suggest dropdown) feature in React. Key evaluation criteria included:
- Efficient API calling (debouncing API requests)
- Handling edge cases (empty input, rapid typing, no results)
- Optimizing for performance
- Accessibility considerations
An example approach for fetching results:
const fetchResults = async (query) => {
const response = await fetch(`https://api.example.com/search?q=${query}`);
return response.json();
};
Debouncing was implemented to prevent excessive API calls:
const debouncedFetch = useCallback(
debounce((query) => fetchResults(query), 300),
[]
);
-
Caching Mechanism in Typeahead: The interviewer inquired about implementing caching for the typeahead feature.
The candidate suggested using a
MaporWeakMapfor in-memory caching:
const cache = new Map();
const getResults = async (query) => {
if (cache.has(query)) return cache.get(query);
const results = await fetchResults(query);
cache.set(query, results);
return results;
};
Follow-up questions addressed cache invalidation strategies and alternative storage solutions like IndexedDB and localStorage.
The candidate successfully cleared this round.
Round 3: Asynchronous Challenges
This round focused on advanced asynchronous JavaScript concepts.
-
Resolve Asynchronous Sequential Promises using Recursion: The challenge involved executing an array of promise-returning functions sequentially.
Initial iterative solution:
const runSequentially = async (functions) => {
for (let func of functions) {
await func();
}
};
The candidate was then asked to implement the same functionality using recursion:
const runSequentiallyRecursive = (functions, index = 0) => {
if (index >= functions.length) return;
functions[index]().then(() => runSequentiallyRecursive(functions, index + 1));
};
- Implement a Cancellable Promise: The task was to create a cancellable promise, allowing the termination of an asynchronous operation before completion.
const makeCancellable = (promise) => {
let isCancelled = false;
const wrappedPromise = new Promise((resolve, reject) => {
promise.then(
(val) => (isCancelled ? reject({ cancelled: true }) : resolve(val)),
(err) => reject(err)
);
});
return { promise: wrappedPromise, cancel: () => (isCancelled = true) };
};
The candidate was unable to effectively implement the cancellable promise wrapper.
The candidate was not successful in this round and was subsequently rejected.
Key Takeaways
- Master Async JavaScript: A strong understanding of promises, async/await, and recursive asynchronous handling is essential for frontend interviews.
- Deep Dive into React: Advanced state management, performance optimizations, and caching strategies are critical.
- Think Performance-First: Web performance is a recurring theme in advanced frontend interviews.
- Practice Regularly: Consistent practice with advanced asynchronous problems is crucial for success.
Original Source
This experience was originally published on medium. Support the author by visiting the original post.
Read on medium