Combination of k elements from an array

combinations.js

const k_combinations = (arr, k) => {
  if (arr.length < k) {
       return [];
  }
  
  if (arr.length === k) {
       return [arr];
  }
      
  if (k === 1) {
       return arr.map(i => [i]);
  }

  const res = [];
  for (let i = 0; i < arr.length; i++) {
    const combinations = k_combinations(arr.slice(i + 1), k - 1);
    for (let j = 0; j < combinations.length; j++) {
      res.push([arr[i], ...combinations[j]]);
    }
  }
  
  return res;
}

const arr = ['a', 'b', 'c', 'd', 'e'];

console.log(k_combinations(arr, 1));
// [["a"],["b"],["c"],["d"],["e"]]
console.log(k_combinations(arr, 2));
// [["a","b"],["a","c"],["a","d"],["a","e"],["b","c"],["b","d"],["b","e"],["c","d"],["c","e"],["d","e"]]
console.log(k_combinations(arr, 3));
// [["a","b","c"],["a","b","d"],["a","b","e"],["a","c","d"],["a","c","e"],["a","d","e"],["b","c","d"],["b","c","e"],["b","d","e"],["c","d","e"]]