nucleotide-count.js

var DNA = function(sequence){
  this.sequence = sequence;
  this.nucleotideCounts = this._countNucleotides();
};

DNA.prototype = {
  count: function(marker){
    this._checkMarker(marker);
    return this.sequence.split(marker).length - 1;
  },

  _countNucleotides: function(){
    var counts = {};
    for(var i = 0; i < this._displayedMarkers.length; i++){
      var marker = this._displayedMarkers[i];
      counts[marker] = this.count(marker);
    }
    return counts;
  },

  _checkMarker: function(marker){
    if(this._acceptedMarkers.indexOf(marker) == -1){
      throw(new Error("Invalid Nucleotide"));
    };    
  },

  _displayedMarkers:  ['A', 'T', 'C', 'G'],
  _acceptedMarkers: DNA.prototype._displayedMarkers + ['U']
}

module.exports = DNA;