Frontend Engineer · Phone Screen · Coding

Confluent — Frontend Engineer ✅ Passed

Level: Mid-Level

Round: Phone Screen · Type: Coding · Difficulty: 6/10 · Duration: 60 min · Interviewer: Very Friendly

Topics: JavaScript, Memoization

Location: Toronto, ON, CA

Interview date: 2025-10-08

Summary

I had a phone screen with a very helpful interviewer. The main question involved implementing a memo function similar to react.memo using JavaScript.

Details

The coding question I received was:

Implement a memo function, similar to react.memo.

Consider the case with one argument: If the argument of the memoized function is the same as before, avoid calling the function and directly return the previously calculated result. You need to store the previously calculated results.

Follow-up questions:

• Consider the case with multiple arguments.
• Consider the case with different argument types.
• Instead of remembering all previous results, only compare with the last calculated result. The argument is an object. How would you compare objects, and how would you compare them if the order doesn't matter?

My Approach:

1. I started by implementing the basic memoization for a single argument, storing the argument and result in a closure.
2. For multiple arguments, I considered using JSON.stringify for simple objects and primitives. I realized this approach would fail for objects with different key orders.
3. For comparing objects when order doesn't matter, I suggested sorting the keys and then stringifying the object. I also discussed using a deep comparison function, but noted its potential performance overhead.

Key Insights:

• Understanding the nuances of object comparison in JavaScript is crucial.
• Being able to discuss the trade-offs between different memoization strategies is important.