concat

The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

const items = [1, 2];

console.log(items.concat(3, 4)); // [1, 2, 3, 4]
console.log(items.concat([3, 4], [5, [6, 7]])); // [1, 2, 3, 4, 5, [6, 7]]