combination-iterative.js

function* combination(array, n) {
  if (n === 1) {
    for (const item of array) yield [item];
    return;
  }

  for (let i = 0; i < array.length - n + 1; i++) {
    const stack = [[[array[i]], array.slice(i + 1)]];
    while (stack.length) {
      const [comb, rest] = stack.shift();
            
      for (let i = 0; i < rest.length; i++) {
        const newComb = [...comb, rest[i]];
        if (newComb.length === n) {
          yield newComb;
          continue;
        } else {
          const newRest = rest.slice(i + 1);
          stack.push([newComb, newRest]);
        }
      }
    }
  }
}

function* combinationAll(array) {
  const { length } = array; 
  for (let i = 1; i <= length; i++) 
  for (const result of combination(array, i)) yield result;
}

console.log('combination', ...combination([1, 2, 3, 4], 3));
console.log('combinationAll', ...combinationAll([1, 2, 3, 4]));