Interview Q&A / System Design
System Design interview questions
Caching, scaling, databases and classic design problems for beginners.
Prefer rapid revision? Practise System Design short interview answers →
- Why must a reducer function be pure, and what breaks if it is not?
React may call a reducer more than once with the same inputs, for example in Strict Mode. A pure reducer returns a new state from state and action only. Mutating state or running side effects inside it gives wrong or duplicated results.
IntermediateQuick answer1 min read