var json = {"obj1":{"prop1":{"prop2":{"prop3":"got it"}}}};

var prop = getByPath('obj1.prop1.prop2.prop3', json);

alert(prop);

function getByPath(path, obj){
	var resultProp = null;
  if(obj && path){
   var pathChain = path.split('.');
   if(pathChain && pathChain > 0){
      var currentProp = obj;
      for(var i=0;i<pathChain.length;i++){
      	if(currentProp[''+pathChain[i]+'']){
          currentProp = obj[''+pathChain[i]+'']
        }else{
          return null;
        }
      }
      return currentProp;
   }
  }
  return resultProp;
}