[JS] Recreate arrayFlat

arrayFlat.js

function arrayFlat(array) {
  return array.reduce((result, elem) => {
    if(Array.isArray(elem)) {
      result.push(...arrayFlat(elem));    
    } 
    else {
      result.push(elem);    
    }
    return result;
  }, []);
}

// ---------------------------------------------- Test ------------------------------------------//
console.log(arrayFlat([]));
console.log(arrayFlat([1]));
console.log(arrayFlat([1,2,3]));
console.log(arrayFlat([[]]));
console.log(arrayFlat([[1,2], []]));
console.log(arrayFlat([[1], [2], [3]]));
console.log(arrayFlat([[1, [2, [3]]], [4, 5]]));