var invert = function (obj) {
  var new_obj = {};
  for (var prop in obj) {
    if(obj.hasOwnProperty(prop)) {
      new_obj[obj[prop]] = prop;
    }
  }
  return new_obj;
};

const data = {
  tea: 3,
  pizza: 2,
  milk: 1
}
const resObj = invert(data);
console.log("resObj", resObj);