JavaScript Arrays: map, filter and reduce

Array methods often make data transformations easier to read. Learn what each one returns before chaining them.

map transforms

map returns an array with one result for each input item. It is appropriate when the number of items remains the same.

filter keeps items for which the callback returns a truthy value. The original array is not modified by filter.

reduce accumulates values into one result such as a sum, dictionary or grouping. Provide an initial value when empty arrays are possible.

Explore a related developer utility and apply what you learned.