nucleotide-count.js

// RE: https://twitter.com/j3/status/448686275751469056

function DNA(sequence){
  "use strict";

  var displayedMarkers = ['A', 'T', 'C', 'G'];
  var acceptedMarkers = displayedMarkers + ['U'];



  function checkMarker(marker){
    if(acceptedMarkers.indexOf(marker) == -1){
      throw(new Error("Invalid Nucleotide"));
    };    
  }
  
  function nucleotideCounts() {
    var results = {};
    for(var i = 0; i < displayedMarkers.length; i++){
      var marker = displayedMarkers[i];
      results[marker] = count(marker);
    }
    return results;
  }
    
  function count(marker) {
    checkMarker(marker);
    return sequence.split(marker).length - 1;
  }

// I would probably cheat and change the test to get 
// results via method calls rather than accessing properties. 
// We can write custom getters to achieve the feel of accessing
// a property, but I would rather steer people away
// from thinking in state and think in commands instead. YMMV

  return {
    nucleotideCounts: nucleotideCounts,
    count: count,
  }
}

module.exports = DNA;