简体中文（ZH-CN）English（EN）繁体中文（ZH-TW）日本語（JA）한국어（KO）Melayu（MS）Français（FR）Deutsch（DE）
Home
Article
Q&A
Course
Topic
Download
Game
Dictionary
Recent Updates

Home  >  Article  >  Web Front-end  >  Use of defineProperty attribute of vue

Use of defineProperty attribute of vue

php中世界最好的语言
php中世界最好的语言Original
2018-06-07 14:49:132845browse

This time I will bring you the use of the defineProperty attribute of vue. What are the precautions for the use of the defineProperty attribute of vue. The following is a practical case, let's take a look.

1. Principle

I believe everyone is familiar with the principle of vue's two-way data binding; mainly through the defineProperty attribute of the ES5 Object object; rewriting data Set and get functions are implemented

, so we will not use ES6 for actual code development; if the function uses the parent this during the process, we should still use the display cache intermediate variables and closures for processing; the reason is The arrow function does not have an independent execution context this; so when the this object appears inside the arrow function, it will directly access the parent; so it can also be seen that the arrow function cannot completely replace the usage scenario of the function; for example, when we need independent this or argument

1.2 What is defineProperty

Syntax:

Object.defineProperty(obj, prop, descriptor)

Parameters:

obj: necessary target object

prop: necessary attribute name that needs to be defined or modified

descriptor: necessary attribute owned by all target attributes

Return value :

Returns the first function passed in; that is, the first parameter obj

This method allows precise addition or modification of the properties of the object; ordinary properties added through assignment will be created in Displayed during attribute enumeration (fon...in; object.key); these added values ​​can be changed or deleted; you can also set some characteristics for this attribute; such as whether it is read-only and not writable; currently there are two forms: Data description (set; get; value; writable; enumerable; confingurable) and accessor description (set; get)

Data description

When modifying or defining the object When a certain attribute; add some characteristics to this attribute

var obj = {
 name:'xiangha'
}
// 对象已有的属性添加特性描述
Object.defineProperty(obj,'name',{
 configurable:true | false, // 如果是false则不可以删除
 enumerable:true | false, // 如果为false则在枚举时候会忽略
 value:'任意类型的值,默认undefined'
 writable:true | false // 如果为false则不可采用数据运算符进行赋值
});
但是存在一个交叉；如果wrirable为true；而configurable为false的时候；所以需要枚举处理enumerable为false
--- 我是一个writable栗子 ---
var obj = {};
Object.defineProperty(obj,'val',{
 value:'xiangha',
 writable:false, // false
 enumerable:true,
 configurable:true
});
obj.val = '书记'; // 这个时候是更改不了a的
--- 我是一个configurable栗子 ---
var obj = {};
Object.defineProperty(obj,'val',{
 value:'xiangha',
 writable:true, // true
 enumerable:true,
 configurable:false // false
});
obj.val = '书记'; // 这个时候是val发生了改变
delete obj.val 会返回false；并且val没有删除
--- 我是一个enumerable栗子 --- 
var obj = {};
Object.defineProperty(obj,'val',{
 value:'xiangha',
 writable:true,
 enumerable:false, // false
 configurable:true
});
for(var i in obj){
 console.log(obj[i]) // 没有具体值
}
综上：对于我们有影响主要是configurable控制是否可以删除；writable控制是否可以修改赋值；enumerable是否可以枚举

So once you use Object.defineProperty() to add attributes to the object; then if you do not set the characteristics of the attribute; the default value is false

var obj = {}; 
Object.defineProperty(obj,'name',{}); // 定义了心属性name后；这个属性的特性的值都为false；这就导致name这个是不能重写不能枚举不能再次设置特性的
obj.name = '书记'; 
console.log(obj.name); // undefined
for(var i in obj){
 console.log(obj[i])
}

Summary features:

  • value: Set the value of the attribute

  • ##writable ['raɪtəbl]: Whether the value can be overridden

  • enumerable [ɪ'nju:mərəbəl]: Whether the target attribute can be enumerated

  • configurable [kən'fɪgərəbl] ]: Whether the target attribute can be deleted and whether the attribute can be modified again

Accessor description

var obj = {};
Object.defineProperty(obj,'name',{
 get:function(){} | undefined,
 set:function(){} | undefined,
 configuracble:true | false,
 enumerable:true | false
})
注意：当前使用了setter和getter方法；不允许使用writable和value两个属性

gettet&& setter

When setting to obtain a certain attribute of the object; you can provide getter and setter methods 

var obj = {};
var value = 'xiangha';
Object.defineProperty(obj,'name',{
 get:function(){
  // 获取值触发
  return value
 }，
 set：function(val){
  // 设置值的时候触发；设置的新值通过参数val拿到
  value = val；
 }
});
console.log(obj.name); // xiangha
obj.name = '书记';
console,.log(obj.name); // 书记
get and set do not have to appear in pairs; just write either one; if you do not set set and set get method; it is undefined

Haha; the foreplay is finally completed

Supplement: If you use vue to develop the project; when you try to print the data object, you will find every attribute in the data Both have get and set attribute methods; here is a description of the difference in two-way data binding between vue and angular

angular uses dirty data detection; when the Model changes, it will detect whether all views are bound to relevant data ; Update the view again

vue uses the publish-subscribe mode; point-to-point binding data

2. Implementation The 

<p id="app">
 <form>
  <input type="text" v-model="number">
  <button type="button" v-click="increment">增加</button>
 </form>
 <h3 v-bind="number"></h3>
 </p>
page is very simple; it contains:

  1. An input, using the v-model instruction

  2. A button, using the v-click instruction

  3. An h3, use the v-bind command.

We will eventually implement two-way data binding in a similar way to vue

var app = new xhVue({
  el:'#app',
  data: {
  number: 0
  },
  methods: {
  increment: function() {
   this.number ++;
  },
  }
 })

2.1 Definition

First we need Define a xhVue constructor

function xhVue(options){
 
}

2.2 Add

In order to initialize this constructor; add an _init attribute to it

function xhVue(options){
 this._init(options);
}
xhVue.prototype._init = function(options){
 this.$options = options; // options为使用时传入的结构体；包括el，data，methods等
 this.$el = document.querySelector(options.el); // el就是#app，this.$el是id为app的Element元素
 this.$data = options.data; // this.$data = {number:0}
 this.$methods = options.methods; // increment
}

2.3 Transformation and upgrade

Transform the _init function; and implement the _xhob function; process data; rewrite the set and get functions

xhVue.prototype._xhob = function(obj){ // obj = {number:0}
 var value;
 for(key in obj){
  if(obj.hasOwnProperty(ket)){
   value = obj[key];
   if(typeof value === 'object'){
    this._xhob(value);
   }
   Object.defineProperty(this.$data,key,{
    enumerable:true,
    configurable:true,
    get:function(){
     return value;
    },
    set:function(newVal){
     if(value !== newVal){
      value = newVal;
     }
    }
   })
  }
 }
}
xhVue.prototype._init = function(options){
 this.$options = options;
 this.$el = document.querySelector(options.el);
 this.$data = options.data;
 this.$method = options.methods;
 this._xhob(this.$data);
}

2.4 xhWatcher

指令类watcher；用来绑定更新函数；实现对DOM更新

function xhWatcher(name,el,vm,exp,attr){
 this.name = name; // 指令名称；对于文本节点；例如text
 this.el = el; // 指令对应DOM元素
 this.vm = vm; // 指令所属vue实例
 this.exp = exp; // 指令对应的值；例如number
 this.attr = attr; // 绑定的属性值；例如innerHTML
 this.update();
}
xhWatcher.prototype.update = function(){
 this.el[this.attr] = this.vm.$data[this.exp];
 // 例如h3的innerHTML = this.data.number;当numner改变则会触发本update方法；保证对应的DOM实时更新
}

2.5 完善_init和_xhob

继续完善_init和_xhob函数

// 给init的时候增加一个对象来存储model和view的映射关系；也就是我们前面定义的xhWatcher的实例；当model发生变化时；我们会触发其中的指令另其更新；保证了view也同时更新
xhVue.prototype._init = function(options){
 this.$options = options;
 this.$el = document.querySelector(options.el);
 this.$data = options.data;
 this.$method = options.methods;
 
 this._binding = {}; // _binding
 this._xhob(this.$data);
}
// 通过init出来的_binding
xhVue.prototype._xhob = function(obj){ // obj = {number:0}
 var value;
 for(key in obj){
  if(obj.hasOwnProperty(ket)){
   this._binding[key] = {
    // _binding = {number:_directives:[]}
    _directives = []
   }
   value = obj[key];
   if(typeof value === 'object'){
    this._xhob(value);
   }
   var binding = this._binding[key];
   Object.defineProperty(this.$data,key,{
    enumerable:true,
    configurable:true,
    get:function(){
     return value;
    },
    set:function(newVal){
     if(value !== newVal){
      value = newVal;
      // 当number改变时；触发_binding[number]._directives中已绑定的xhWatcher更新
      binding._directives.forEach(function(item){
       item.update(); 
      });
     }
    }
   })
  }
 }
}

2.6 解析指令

怎么才能将view与model绑定；我们定义一个_xhcomplie函数来解析我们的指令（v-bind；v-model；v-clickde）并这这个过程中对view和model进行绑定

xhVue.prototype._xhcompile = function (root) {
 // root是id为app的element的元素；也就是根元素
 var _this = this;
 var nodes = root.children;
 for (var i = 0,len = nodes.length; i < len; i++) {
  var node = nodes[i];
  if (node.children.length) {
   // 所有元素进行处理
   this._xhcompile(node)
  };
  // 如果有v-click属性；我们监听他的click事件；触发increment事件，即number++
  if (node.hasAttribute(&#39;v-click&#39;)) {
   node.onclick = (function () {
    var attrVal = nodes[i].getAttribute(&#39;v-click&#39;);
    // bind让data的作用域与methods函数的作用域保持一致
    return _this.$method[attrVal].bind(_this.$data);
   })();
  };
  // 如果有v-model属性；并且元素是input或者textrea；我们监听他的input事件
  if (node.hasAttribute(&#39;v-model&#39;) && (node.tagName = &#39;INPUT&#39; || node.tagName == &#39;TEXTAREA&#39;)) {
   node.addEventListener(&#39;input&#39;, (function (key) {
    var attrVal = node.getAttribute(&#39;v-model&#39;);
    _this._binding[attrVal]._directives.push(new xhWatcher(
     &#39;input&#39;, 
     node, 
     _this,
     attrVal, 
     &#39;value&#39;
    ));
    return function () {
     // 让number的值和node的value保持一致；就实现了双向数据绑定
     _this.$data[attrVal] = nodes[key].value
    }
   })(i));
  };
  // 如果有v-bind属性；我们要让node的值实时更新为data中number的值
  if (node.hasAttribute(&#39;v-bind&#39;)) {
   var attrVal = node.getAttribute(&#39;v-bind&#39;);
   _this._binding[attrVal]._directives.push(new xhWatcher(
    &#39;text&#39;, 
    node, 
    _this,
    attrVal,
    &#39;innerHTML&#39;
   ))
  }
 }
}

并且将解析函数也加到_init函数中

xhVue.prototype._init = function(options){
 this.$options = options;
 this.$el = document.querySelector(options.el);
 this.$data = options.data;
 this.$method = options.methods;
 
 this._binding = {}; // _binding
 this._xhob(this.$data);
 this._xhcompile(this.$el);
}

最后

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>Document</title>
</head>
<body>
 <p id="app">
  <form>
   <input type="text" v-model="number">
   <button type="button" v-click="increment">增加</button>
  </form>
  <h3 v-bind="number"></h3>
 </p>
</body>
<script>
 function xhVue(options) {
  this._init(options);
 }
 xhVue.prototype._init = function (options) {
  this.$options = options;
  this.$el = document.querySelector(options.el);
  this.$data = options.data;
  this.$method = options.methods;
  this._binding = {}; // _binding
  this._xhob(this.$data);
  this._xhcompile(this.$el);
 }
 xhVue.prototype._xhob = function (obj) {
  var value;
  for (key in obj) {
   if (obj.hasOwnProperty(key)) {
    this._binding[key] = {
     _directives: []
    }
    value = obj[key];
    if (typeof value === 'object') {
     this._xhob(value);
    }
    var binding = this._binding[key];
    Object.defineProperty(this.$data, key, {
     enumerable: true,
     configurable: true,
     get: function () {
      console.log(`get${value}`)
      return value;
     },
     set: function (newVal) {
      if (value !== newVal) {
       value = newVal;
       console.log(`set${newVal}`)
       // 当number改变时；触发_binding[number]._directives中已绑定的xhWatcher更新
       binding._directives.forEach(function (item) {
        item.update();
       });
      }
     }
    })
   }
  }
 }
 xhVue.prototype._xhcompile = function (root) {
  // root是id为app的element的元素；也就是根元素
  var _this = this;
  var nodes = root.children;
  for (var i = 0, len = nodes.length; i < len; i++) {
   var node = nodes[i];
   if (node.children.length) {
    // 所有元素进行处理
    this._xhcompile(node)
   };
   // 如果有v-click属性；我们监听他的click事件；触发increment事件，即number++
   if (node.hasAttribute(&#39;v-click&#39;)) {
    node.onclick = (function () {
     var attrVal = node.getAttribute(&#39;v-click&#39;);
     console.log(attrVal);
     // bind让data的作用域与method函数的作用域保持一致
     return _this.$method[attrVal].bind(_this.$data);
    })();
   };
   // 如果有v-model属性；并且元素是input或者textrea；我们监听他的input事件
   if (node.hasAttribute(&#39;v-model&#39;) && (node.tagName = &#39;INPUT&#39; || node.tagName == &#39;TEXTAREA&#39;)) {
    node.addEventListener(&#39;input&#39;, (function (key) {
     var attrVal = node.getAttribute(&#39;v-model&#39;);
     _this._binding[attrVal]._directives.push(new xhWatcher(
      &#39;input&#39;,
      node,
      _this,
      attrVal,
      &#39;value&#39;
     ));
     return function () {
      // 让number的值和node的value保持一致；就实现了双向数据绑定
      _this.$data[attrVal] = nodes[key].value
     }
    })(i));
   };
   // 如果有v-bind属性；我们要让node的值实时更新为data中number的值
   if (node.hasAttribute(&#39;v-bind&#39;)) {
    var attrVal = node.getAttribute(&#39;v-bind&#39;);
    _this._binding[attrVal]._directives.push(new xhWatcher(
     &#39;text&#39;,
     node,
     _this,
     attrVal,
     &#39;innerHTML&#39;
    ))
   }
  }
 }
 function xhWatcher(name, el, vm, exp, attr) {
  this.name = name; // 指令名称；对于文本节点；例如text
  this.el = el; // 指令对应DOM元素
  this.vm = vm; // 指令所属vue实例
  this.exp = exp; // 指令对应的值；例如number
  this.attr = attr; // 绑定的属性值；例如innerHTML
  this.update();
 }
 xhWatcher.prototype.update = function () {
  this.el[this.attr] = this.vm.$data[this.exp];
  // 例如h3的innerHTML = this.data.number;当numner改变则会触发本update方法；保证对应的DOM实时更新
 }
 var app = new xhVue({
  el: &#39;#app&#39;,
  data: {
   number: 0
  },
  methods: {
   increment: function () {
    this.number++;
   }
  }
 });
</script>
</html>

相信看了本文案例你已经掌握了方法，更多精彩请关注php中文网其它相关文章！

推荐阅读：

怎样使用jQuery滚动条美化插件nicescroll

Angular中怎样调用第三方库

The above is the detailed content of Use of defineProperty attribute of vue. For more information, please follow other related articles on the PHP Chinese website!

Statement：
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Previous article：Two methods to implement pop-up window functionNext article：Two methods to implement pop-up window function

Related articles

See more