var Map = function() {
  this.collection = {};
  // change code below this line
  this.add = function(key, val){
      this.collection[key] = val;
  }
  
  this.remove = function(key){
      delete this.collection[key];
  }
  
  this.get = function(key){
      return this.collection[key];
  }
  
  this.has = function(key){
      return typeof this.collection[key] == 'undefined' ? false : true;
  }
  
  this.values = function(){
      var val = '';
      for(var p in this.collection){
          val += this.collection[p];
      }
      return val;
  }
  
  this.clear = function(){
    this.collection = {};
  }
  
  this.size = function(){
      var len = 0;
      
      for(var p in this.collection){
          len++;
      }
      
      return len;
  }
  // change code above this line
};