Removing all that this. Alternate version of https://github.com/jcasimir/exercism_solutions/blob/master/javascript/nucleotide-count/nucleotide-count.js

nucleotide-count.js

var DNA = function(sequence) {
  var count, checkMarker;
  var nucleotideCounts = {};
  var displayedMarkers = ['A', 'T', 'C', 'G'];
  var acceptedMarkers = displayedMarkers + ['U'];
  
  count = function(marker){
    checkMarker(marker);
    return sequence.split(marker).length - 1;
  }
  
  checkMarker = function(marker){
    if(acceptedMarkers.indexOf(marker) == -1){
      throw(new Error("Invalid Nucleotide"));
    }
  }

  for(var i = 0; i < displayedMarkers.length; i++){
    var marker = displayedMarkers[i];
    nucleotideCounts[marker] = count(marker);
  }
  
  return {
    count: function(marker) {
      return count(marker)
    },
    nucleotideCounts: nucleotideCounts
  }
}