function fibonacci(n, memo = {}) { if (n in memo) return memo[n]; if (n <= 2) return 1; memo[n] = fibonacci(n - 1, memo) + fibonacci(n - 2, memo); return memo[n]; } console.log(fibonacci(10)); // Outputs: 55

What is memoisation?

Difficulty: 5/10

caching, pure functions, performance

Memoization is an optimization technique used to store the results of expensive function calls and return the cached result when the same inputs occur again. It can greatly improve the performance of functions that are repeatedly called with the same arguments.

javascript

Scenario Questions

0-2 years experience

1We have a recursive function that calculates the nth Fibonacci number. How would you add memoisation in JavaScript to make it run faster?
2If you call a memoised function twice with the same arguments, what does it return and why?
3What could happen to memory usage if a memoised cache never gets cleared in a single‑page app?

2-5 years experience

Follow-up Questions