适用 prototype 属性给对象添加属性 - 在线编辑器

          <script>
  function employee(name, jobtitle, born) {
    this.name = name;
    this.jobtitle = jobtitle;
    this.born = born;
  }
  var fred = new employee("Fred Flintstone", "Caveman", 1970);
  employee.prototype.salary = null;
  fred.salary = 20000;
  document.write(fred.salary);
</script>
        