Interview Experience: Senior Frontend Engineer at Quizizz

Overview

A candidate recently underwent the interview process for a Senior Frontend Engineer position at Quizizz. The process comprised four stages, evaluating the candidate's expertise in JavaScript fundamentals, problem-solving, low-level design, and behavioral aspects. Although the candidate was not offered the position, the interview experience provided significant learning opportunities.

Interview Rounds

Round 1: JavaScript Fundamentals & Problem-Solving

This round heavily emphasized JavaScript knowledge, featuring a combination of theoretical and practical coding questions.

1. JavaScript Concepts: The candidate was questioned on core JavaScript concepts, including execution context and call stack management, prototypes and closures, the event loop and its handling of asynchronous operations, and the differences and best practices related to Promises and async/await.

2. Currying Function Implementation: The candidate was tasked with implementing a currying function. The solution required overriding the valueOf method to ensure correct evaluation during arithmetic operations.

   function currying(a) {
       return function next(b) {
           if (b === undefined) return a;
           a += b;
           next.valueOf = function() { return a; }; // Ensuring correct implicit conversion
           return next;
       };
   }
   

3. Promises & Async/Await Implementation: The candidate was first asked to predict the output of a code snippet involving Promises and async/await. Subsequently, the candidate was required to implement a feature utilizing Promises, focusing on correct chaining and efficient error handling.

Round 2: Coding Challenge

The candidate faced a coding challenge centered on JavaScript functional programming, demanding efficient state management and computations. Key areas assessed included immutable state updates, functional composition for reusable solutions, and performance optimization to reduce unnecessary computations. Time constraints added to the challenge.

Round 3: Low-Level Design (LLD)

This round presented the most significant challenge, requiring the candidate to design an Excel-like system. The evaluation focused on:

1. Data Structure Design: Efficient storage and retrieval of cell values, including handling formulas and dependencies (e.g., A1 = B1 + C1).
2. Dependency Management: Designing a mechanism for propagating changes, such as automatically updating A1 when B1 is modified in the scenario A1 = B1 + C1.
3. Performance Considerations: Implementing efficient recalculations to avoid unnecessary computations and optimizing performance for large spreadsheets.

The candidate encountered difficulties in defining an optimal data structure for storing dependencies and the proposed solution lacked caching mechanisms.

Round 4: Behavioral

This round focused on the candidate's project contributions, ownership, and experience. The interviewer inquired about major projects, the candidate's role in decision-making, and instances where the candidate improved performance, scalability, or user experience. The candidate also discussed responsibilities in their current company, including frontend architecture, performance optimizations, and collaboration with backend teams. Follow-up technical questions were posed to assess the candidate's thought process behind technical decisions.

Key Takeaways

Although the candidate was not selected due to challenges in the low-level design round, particularly in efficiently handling dependencies, the interview process yielded valuable learning experiences. The candidate gained insights into approaching system design problems in a structured manner, recognized the importance of choosing appropriate data structures in LLD, and deepened their understanding of JavaScript fundamentals.