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Starter#Arrays#Polyfill
Array.prototype.map Polyfill
Implement Array.prototype.map from scratch. Master callback signatures, thisArg binding, and sparse-array hole preservation.
By modernDev2026-06-05Easy
Rebuilding map forces you to think about what it actually does: call a function on every element, collect the results in a new array, and never touch the original. The details that trip people up are passing all three arguments to the callback (element, index, array), supporting the optional thisArg, and preserving holes in sparse arrays.
Goal: Implement myMap in under 15 minutes. Make sure all three callback arguments work and thisArg is respected.
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