Combination

const makingComb = (arr, leng) => {
  const result = [];
  
  if(leng === 1) return arr.map(i => [i]);
  
  arr.forEach((fixed, idx, arr) => {
    const combination = makingComb(arr.slice(idx + 1), leng - 1);
    const attached = combination.map(i => [fixed, ...i]);
    result.push(...attached);
  }) 
  
  return result;
}

makingComb([1, 2, 3, 1, 2, 3, 4], 4);

//result
[
  [ 1, 2, 3, 1 ], [ 1, 2, 3, 2 ], [ 1, 2, 3, 3 ],
  [ 1, 2, 3, 4 ], [ 1, 2, 1, 2 ], [ 1, 2, 1, 3 ],
  [ 1, 2, 1, 4 ], [ 1, 2, 2, 3 ], [ 1, 2, 2, 4 ],
  [ 1, 2, 3, 4 ], [ 1, 3, 1, 2 ], [ 1, 3, 1, 3 ],
  [ 1, 3, 1, 4 ], [ 1, 3, 2, 3 ], [ 1, 3, 2, 4 ],
  [ 1, 3, 3, 4 ], [ 1, 1, 2, 3 ], [ 1, 1, 2, 4 ],
  [ 1, 1, 3, 4 ], [ 1, 2, 3, 4 ], [ 2, 3, 1, 2 ],
  [ 2, 3, 1, 3 ], [ 2, 3, 1, 4 ], [ 2, 3, 2, 3 ],
  [ 2, 3, 2, 4 ], [ 2, 3, 3, 4 ], [ 2, 1, 2, 3 ],
  [ 2, 1, 2, 4 ], [ 2, 1, 3, 4 ], [ 2, 2, 3, 4 ],
  [ 3, 1, 2, 3 ], [ 3, 1, 2, 4 ], [ 3, 1, 3, 4 ],
  [ 3, 2, 3, 4 ], [ 1, 2, 3, 4 ]
]

출처1
출처2