array-methodseasy
When would you use map, filter and reduce?
Answer
map transforms every item and returns a new array of the same length. filter keeps the items that pass a test, so the result is the same or shorter. reduce folds the array into a single accumulated value — a total, a grouping, or even a rebuilt object. All three return new values rather than mutating, which is what makes them safe to chain.
Points an interviewer listens for
- map: same length, transformed items
- filter: subset, same items
- reduce: many values folded into one
- None mutate the source array
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