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Vue data-driven simulation implementation 1

高洛峰

Jan 12, 2017 pm 01:54 PM

一、前言

Vue有一核心就是数据驱动（Data Driven），允许我们采用简洁的模板语法来声明式的将数据渲染进DOM，且数据与DOM是绑定在一起的，这样当我们改变Vue实例的数据时，对应的DOM元素也就会改变了。

如下：

<!DOCTYPE html>
<head>
 <meta charset="utf-8">
</head>
 <body>
  <div id="test">
   {{name}}
  </div>
  <script src="https://unpkg.com/vue/dist/vue.min.js"></script>
  <script>
   var vm = new Vue({
    el: &#39;#test&#39;,
    data: {
     name: &#39;Monkey&#39;
    }
   });
  </script>  
 </body>
</html>

当我们在chrome控制台，更改vm.name时，页面中的数据也随之改变，但我们并没有与DOM直接接触

好了，今儿的核心就是模拟上述Demo中的数据驱动。

二、模拟Vue之数据驱动

通过粗浅地走读Vue的源码，发现达到这一效果的核心思路其实就是利用ES5的defineProperty方法，监听data数据，如果数据改变，那么就对页面做相关操作。

有了大体思路，那么我们就开始一步一步实现一个简易版的Vue数据驱动吧，简称SimpleVue。

Vue实例的创建过程，如下：

var vm = new Vue({
 el: &#39;#test&#39;,
 data: {
  name: &#39;Monkey&#39;
 }
});

因此，我们也依瓢画葫芦，构建SimpleVue构造函数如下：

function SimpleVue(obj){
 this.$el = document.querySelector(obj.el);
 this.$options = obj;
 this._data = Object.create(null);
 //入口
 this.init();
 obj = null;
};
SimpleVue.prototype = {
 constructor: SimpleVue,
 init: function(){
  //TODO
 }
};

接下来，我们在SimpleVue原型上编写一个watchData方法，通过利用ES5原生的defineProperty方法，监听data中的属性，如果属性值改变，那么我们就进行相关的页面处理。

如下：

SimpleVue.prototype = {
 //监听data属性
 watchData: function(){
  var data = this.$options.data,//得到data对象
   keys = Object.keys(data),//data对象上全部的自身属性，返回数组
   that = this;
  keys.forEach(function(elem){//监听每个属性
   Object.defineProperty(that, elem, {
    enumerable: true,
    configurable: true,
    get: function(){
     return that._data[elem];
    },
    set: function(newVal){
     that._data[elem] = newVal;
     that.update();//数据变化，更新页面
    }
   });
   that[elem] = data[elem];//初次进入改变that[elem]，从而触发update方法
  });
 }
};

好了，如果我们检测到数据变化了呢？

那么，我们就更新视图嘛。

但是，怎么更新呢？

简单的实现方式就是，在初次构建SimpleVue实例时，就将页面中的模板保存下来，每次实例数据一改变，就通过正则替换掉原始的模板，即双括号中的变量，如下：

 SimpleVue.prototype = {
 //初始化SimpleVue实例时，就将原始模板保留
 getTemplate: function(){
  this.template = this.$el.innerHTML;
 },
 //数据改变更新视图
 update: function(){
  var that = this,
   template = that.template,
   reg = /(.*?)\{\{(\w*)\}\}/g,
   result = &#39;&#39;;
  result = template.replace(reg, function(rs, $1, $2){
   var val = that[$2] || &#39;&#39;;
   return $1 + val;
  });
  this.$el.innerHTML = result;
  console.log(&#39;updated&#39;);
 }
};

好了，整合上述js代码，完整的SimpleVue如下：

function SimpleVue(obj){
 this.$el = document.querySelector(obj.el);
 this.$options = obj;
 this._data = Object.create(null);
 //入口
 this.init();
 obj = null;
};
SimpleVue.prototype = {
 constructor: SimpleVue,
 init: function(){
  this.getTemplate();
  this.watchData();
 },
 //初始化SimpleVue实例时，就将原始模板保留
 getTemplate: function(){
  this.template = this.$el.innerHTML;
 },
 //监听data属性
 watchData: function(){
  var data = this.$options.data,//得到data对象
   keys = Object.keys(data),//data对象上全部的自身属性，返回数组
   that = this;
  keys.forEach(function(elem){//监听每个属性
   Object.defineProperty(that, elem, {
    enumerable: true,
    configurable: true,
    get: function(){
     return that._data[elem];
    },
    set: function(newVal){
     that._data[elem] = newVal;
     that.update();//数据变化，更新页面
    }
   });
   that[elem] = data[elem];
  });
 },
 //数据改变更新视图
 update: function(){
  var that = this,
   template = that.template,
   reg = /(.*?)\{\{(\w*)\}\}/g,
   result = &#39;&#39;;
  result = template.replace(reg, function(rs, $1, $2){
   var val = that[$2] || &#39;&#39;;
   return $1 + val;
  });
  this.$el.innerHTML = result;
  console.log(&#39;updated&#39;);
 }
};

测试代码如下：

<!DOCTYPE html>
<head>
 <meta charset="utf-8">
</head>
 <body>
  <div id="test">
   <div>{{name}}</div>
  </div>
  <script src="./SimpleVue.js"></script>
  <script>
   var vm = new SimpleVue({
    el: &#39;#test&#39;,
    data: {
     name: &#39;Monkey&#39;
    }
   });
  </script> 
 </body>
</html>

效果如下：

Vue data-driven simulation implementation 1

三、优化

上述实现效果，还不错哦。

但是，我们走读下上述代码，感觉还可以优化下。

（1）、在watchData方法中监听每个data属性时，如果我们设置相同值，页面也会更新的，因为set是监听赋值的，它又不知道是不是同一个值，因此，优化如下：

Vue data-driven simulation implementation 1

（2）、在上述基础，我们加入了新旧值判断，但是如果我们频繁更新data属性呢？那么也就会频繁调用update方法。例如，当我们给vm.name同时赋值两个值时，页面就会更新两次，如下：

Vue data-driven simulation implementation 1

怎么解决呢？

利用节流，即可：

SimpleVue.throttle = function(method, context, delay){
 clearTimeout(method.tId);
 method.tId = setTimeout(function(){
  method.call(context);
 }, delay);
};

好了，将优化点整合到原有代码中，得下:

function SimpleVue(obj){
 this.$el = document.querySelector(obj.el);
 this.$options = obj;
 this._data = Object.create(null);
 this.init();
 obj = null;
};
SimpleVue.throttle = function(method, context, delay){
 clearTimeout(method.tId);
 method.tId = setTimeout(function(){
  method.call(context);
 }, delay);
};
SimpleVue.prototype = {
 constructor: SimpleVue,
 init: function(){
  this.getTemplate();
  this.watchData();
 },
 getTemplate: function(){
  this.template = this.$el.innerHTML;
 },
 watchData: function(){
  var data = this.$options.data,
   keys = Object.keys(data),
   that = this;
  keys.forEach(function(elem){
   Object.defineProperty(that, elem, {
    enumerable: true,
    configurable: true,
    get: function(){
     return that._data[elem];
    },
    set: function(newVal){
     var oldVal = that[elem];
     if(oldVal === newVal){
      return;
     }
     that._data[elem] = newVal;
     SimpleVue.throttle(that.update, that, 50);
    }
   });
   that[elem] = data[elem];
  });
 },
 update: function(){
  var that = this,
   template = that.template,
   reg = /(.*?)\{\{(\w*)\}\}/g,
   result = &#39;&#39;;
  result = template.replace(reg, function(rs, $1, $2){
   var val = that[$2] || &#39;&#39;;
   return $1 + val;
  });
  this.$el.innerHTML = result;
  console.log(&#39;updated&#39;);
 }
};

且，为了让我们使用更加方便，我们可以在上述代码基础上，加入一个created钩子（当然，你可以加入更多），完整代码见github。

好了，简单的数据驱动，我们算实现了，也优化了，但，其实上述简易版Vue有很多问题，例如：

1）、监听的属性是个对象呢？且对象里又有其他属性，不就监听不成功了么？如下：

Vue data-driven simulation implementation 1

2）、通过上述1）介绍，如果监听的属性是个对象，那么又该如何渲染DOM呢？

3）、渲染DOM我们采用的是innerHTML，那么随着DOM的扩大，性能显而易见，又该如何解决？

等等问题，我们将在后续随笔通过精读源码，一步一步完善。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持PHP中文网。

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