array_permutations.js

/**
  * Given an array of size 'n' and a number 'r' (r <= n), this generator returns all 
  * nCr permutation subarrays of the array.
  * 
  * @param arr - array
  * @param r number
*/
function* permutations(arr, r, prefix = []) {
  for (let i = 0; i < arr.length - r + 1; i++) {
    let x = [...prefix, arr[i]]
    if (r > 1)
      yield* permutations(arr.slice(i + 1), r - 1, x)
    else
      yield x 
  }
}