concat and flat multi diminsional array code example

Example 1: array flatten

const arr = [1, 2, [3, 4]];

// To flat single level array
arr.flat();
// is equivalent to
arr.reduce((acc, val) => acc.concat(val), []);
// [1, 2, 3, 4]

// or with decomposition syntax
const flattened = arr => [].concat(...arr);

Example 2: js ,flat

const numbers = [1, 2, [3, 4, 5, [6, 7]]];
const flatNumbers = numbers.flat(2);

console.log(flatNumbers);