JavaScript Accessor

function Model(){
  
  var data = {};
  
  // accessor
  this.data = function(name, value){
    // null makes it a deleter
    if(null === value) {
      delete data[name];
      return this;
    }
    // undefined makes it a getter
    if('undefined' === typeof value){
      return value;
    }
    
    // primitive or object make it a setter
    data[name] = value;
    return this;
    
  }

}