JSFiddle - React, Tailwind, and code Playground

JavaScript

function repeat(a, n, r) {
    return !n ? r : repeat(a, --n, (r||[]).concat(a));
}
    
console.log(repeat([1,2,3], 4)); // [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3]