var test = {
   _age: 18,
   get age() {
     console.log('触发get');
     //直接会this.age会进入死递归的
     return this._age;
   },
   set age(age) {
     console.log('触发set');
     this._age = age;
   }
 };

 var _age = 18;
 var test = {
   get age() {
     console.log('触发get');
     //直接会this.age会进入死递归的
     return _age;
   },
   set age(age) {
     console.log('触发set');
     _age = age;
   }
 };

 function test() {
   var _age = 18;
   Object.defineProperty(this, "age", {
     get: function () {
       console.log('触发get');
       return _age;
     },
     set: function (value) {
       console.log('触发set')
       _age = value;
     }
   });
 }
 var t = new test();
 t.age=18;

<div id="test">
  <p>name:</p>
  <p>age:</p>
</div>

function Element(id, initData) {
  var self = this;
  var el = document.getElementById(id);
  var templet = el.innerHTML;
  var _data = null;

  if (initData) {
    _data = {};
    for (var variable in initData) {
      _data[variable] = initData[variable];
      bind(variable, self);
    }
  }

  function bind(variable, obj) {
    Object.defineProperty(self, variable, {
      set: function (value) {
        //使用_data里的数据，避免死递归
        _data[variable] = value;
        //每次被设置新值的时候重新渲染界面
        render();
      },
      get: function () {
        return _data[variable];
      },
    });
  }

  //渲染
  function render() {
    var temp = templet;
    temp = temp.replace(/\{\{(.*)\}\}/g, function (s, t) {
      if (_data[t]) {
        return _data[t];
      }
    });
    el.innerHTML = temp;
  }

  //初始化时候手动渲染一次
  render();
}

var app = new Element('test', {
  name: 'zhangsan',
  age: 18
})

<div id="test">
  <input type="text" value="">
  <br>
  <span></span>
</div>

function Element(id, initData) {
  var self = this;
  var el = document.getElementById(id);
  var templet = el.innerHTML;
  var input = el.getElementsByTagName('input')[0];
  var _data = initData;

  Object.defineProperty(self, 'data', {
    set: function (value) {
      _data = value;
      render();
    },
    get: function () {
      return _data;
    },
  });

  //渲染
  function render() {
    var temp = templet;
    temp = temp.replace(/\{\{(data)\}\}/g, function (s, t) {
      return _data;
    });
    el.innerHTML = temp;

    //重新添加事件，其实应该用事件委托的
    input = el.getElementsByTagName('input')[0];
    inputchange();
    input.focus();
  }

  function inputchange() {
    if (window.attachEvent) {
      input.attachEvent("oninput", temp);
    } else if (window.addEventListener) {
      input.addEventListener("input", temp, false);
    }

    function temp() {
      self.data = input.value;
    }
  }

  //初始化时候手动渲染一次
  render();
}
var app = new Element('test', '');