const nestedArray = [1, [2], [[3], 4], 5]; const flatten = nestedArray => nestedArray.reduce( (flat, item) => flat.concat(Array.isArray(item) ? flatten(item) : [item]), [] ); flatten(nestedArray);
const nestedArray = [1, [2], [[3], 4], 5]; const flatten = nestedArray => nestedArray.reduce( (flat, item) => flat.concat(Array.isArray(item) ? flatten(item) : [item]), [] ); flatten(nestedArray);