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What do flat and flatMap do?

Q: What do flat and flatMap do?

**Core concept (TL;DR).** flat(depth) returns a new array with nested sub-arrays flattened up to depth levels (default 1 ; pass Infinity to fully flatten). flatMap(fn) is map followed by a single level of flat — ideal for mapping where each item can expand to zero, one, or many results. flat lowers nesting · flatMap = map + flat(1) [1, [2, 3], [4]]</t

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