Sum of combinations

Possible Combintation Sum

// requires an array sorted in ascending order

var possibleCombinationSum = function(arr, n) {
  // easiest case: n is in the array somewhere
  if (arr.indexOf(n) >= 0) { return true; }
  // if the smallest element is > n, no solution, so finish
  if (arr[0] > n) { return false; }
  // get rid of any elements larger than n, recursively
  if (arr[arr.length - 1] > n) {
    arr.pop();
    return possibleCombinationSum(arr, n);
  }

  var listSize = arr.length, combinationsCount = (1 << listSize)
  for (var i = 1; i < combinationsCount ; i++ ) {
    var combinationSum = 0;
    for (var j=0 ; j < listSize ; j++) {
      if (i & (1 << j)) { combinationSum += arr[j]; }
    }
    if (n === combinationSum) { return true; }
  }
  return false;
};