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JavaScript interview question
Intersection By
medium20 min
Find unique values shared by every input array, comparing values through a derived key.
Requirements
Implement intersectionBy(arrays, iteratee), where arrays is an array of dense arrays and iteratee is a callback or a direct property key. This explicit array-of-arrays signature supports any number of inputs.
Return original values from the first array whose computed keys occur in every array. Keep first-array order, and include only the earliest first-array item for each shared key.
Compare keys using SameValueZero, as Set does: NaN matches NaN, 0 matches -0, and objects/symbols compare by identity. Do not stringify keys or deeply compare them.
A callback receives only the value. For nonempty inputs, evaluate it once per item, caching the derived keys. Property-key iteratees read the direct property, including symbols.
Zero input arrays or any empty input array return a fresh empty array without calling the iteratee. A single input array returns its values deduplicated by key. Do not mutate input, clone returned values, or hide callback errors.
