Remove from object all keys who aren't on the array.

Object.prototype.only.js

(function(window) {
  var only = function (keep) {
    var obj = this;
    
    Object.keys(obj).forEach(function(key) {
      if(keep.indexOf(key) === -1)
        obj.delete(key);
    });  
    
    return obj;
  };

  Object.prototype.delete = function (name) {
    delete this[name];
  };
	
  if ('defineProperty' in Object) {
    Object.defineProperty(Object.prototype, 'only', {
      value: only,
      enumerable: false
    });
  } else {
    Object.prototype.only = only;
  }
})(window);

Funciona melhor:
https://gist.github.com/darlanalves/32edfa35937cde1ca4fb