Arrays & Array Methods (map, filter, reduce)

const nested = [[1, 2], [3, 4], [5, 6]];
const flattened = nested.reduce((flat, curr) => flat.concat(curr), []);

Sorting the nested arrays
Summing all numbers
Flattening the nested array
This reduce operation flattens a nested array: 1) Uses concat to combine arrays progressively, 2) Initial value [] serves as starting point, 3) Each iteration concatenates current subarray to accumulated result, 4) Transforms [[1,2],[3,4],[5,6]] to [1,2,3,4,5,6], 5) Alternative to using flat() method, 6) Works for one level of nesting, 7) Can be modified for deep flattening, 8) Common pattern for array structure transformation.
Counting array elements