number-of-cases-by-count-iterative.js

function* numberOfCases(array, count) {
  const stack = [[[], array]];
  let target;
  while (target = stack.shift()) {
    const [c, rest] = target;
    if (c.length === count) yield c;
    else stack.push(...rest.map((item, i) => [[...c, item], rest.filter((_, j) => j !== i)]));
  }
}

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

console.log('numberOfCasesByCount', ...numberOfCases([2,4,6,8,10], 3));
console.log('numberOfCases', ...numberOfCasesAll([1,2,3]));