code: function deepDiff(a, b, r, reversible) {
  	_.each(a, function(v, k) {
  	  // already checked this or equal...
  	  if (r.hasOwnProperty(k) || b[k] === v) return;
  	  // but what if it returns an empty object? still attach?
  	  r[k] = _.isObject(v) ? _.diff(v, b[k], reversible) : v;
  	});
  }
docs: /*
  From here:
  http://jsfiddle.net/drzaus/9g5qoxwj/