Flatten deeply in JavaScript
JavaScript interview exercise on Arrays, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Write flattenDeep(arr) that flattens any depth of nesting into a single array. Do it recursively without flat(Infinity).
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.