just-flatten-it Part of a library of zero-dependency npm modules that do just do one thing. Guilt-free utilities for every occasion. Try it now import flatten from 'just-flatten-it'; flatten([[1, [2, 3]], [[4, 5], 6, 7, [8, 9]]]); // [1, 2, 3, 4, 5, 6, 7, 8, 9]