GeneralFrontend
Immutability
Also written as Immutable Data, Pure Function, Side Effect
Designing data so it's never modified in place — changes produce a new copy. Makes code far easier to reason about, especially with concurrency.
Think of it like
Writing a new version of a document rather than editing the original with everyone watching.
Junior or senior?
Junior sounds like
Knows React state should be replaced not mutated.
Senior sounds like
Connects it to concurrency, caching, or debugging — why it matters beyond the framework rule.
Ask them
“Where has immutability actually saved you from a bug?”