Do map, filter, and reduce mutate the original array in JavaScript?
No. All three return new values (a new array for map and filter, a single value for reduce). The original array is unchanged.
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More FAQs in map, filter, and reduce in JavaScript: A Complete Guide
map transforms each element and returns a new array of the same length. filter selects elements that pass a test and returns a shorter (or equal) array. reduce combines all elements into a single value using an accumulator.
map and filter callbacks receive (element, index, array). reduce callback receives (accumulator, element, index, array). Most callbacks only use the first one or two, but all are available.
Yes. map and filter return new arrays, so you can chain them. reduce returns a single value, so it is usually last. Example: arr.filter(n => n > 1).map(n => n * 2).reduce((a, b) => a + b, 0).
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