en.javascript.info/1-js/4-data-structures/5-object-for-in/1-is-empty/solution.md

function isEmpty(obj) {
  for (var key in obj) {
    return false;
  }
  return true;
}

var schedule = {};

alert( isEmpty(schedule) ); // true

schedule["8:30"] = "подъём";

alert( isEmpty(schedule) ); // false