How to perform mvvm-simple two-way binding in actual projects
这次给大家带来怎样在实战项目中进行mvvm-simple双向绑定，在实战项目中进行mvvm-simple双向绑定的注意事项有哪些，下面就是实战案例，一起来看一下。
mvvm模式解放DOM枷锁
mvvm原理分析
JavaScript在浏览器中操作HTML经历了几个不同阶段
第一阶段 直接用浏览器提供的原生API操作DOM元素
var dom = document.getElementById('id');
dom.innerHTML = 'hello mvvm';第二阶段 jQuery的出现解决了原生API的复杂性和浏览器间的兼容性等问题，提供了更加简易方便的API
$('#id').text('hello mvvm')第三阶段 MVC模式使前端可以和后端配合，修改服务端渲染后的页面内容
而随着产品对于用户体验的重视，交互体验越来越重要，仅用jQuery远远不够。 MVVM模型解决了频繁操作的痛点，Model-View-ViewModel模式将数据与视图的同步交由ViewModel完成
jQuery修改节点内容:
<p>name: <span id="name">vist</span>!</p>
<p>age: <span id="age">25</span>.</p>
var name = 'bestvist';
var age = 26;
$('#name').text(name);
$('#age').text(age);MVVM模式下只需要关注数据结构:
var me = {
name: 'vist',
age: 25
}修改相应属性就好
me.name = 'bestvist'; me.age = 26;
mvvm实现
mvvm实现数据绑定的几种方式：
发布-订阅模式
脏值检查
数据劫持
比较流行的vue采用的就是数据劫持和发布-订阅模式，通过劫持es5提供的Object.defineProperty()中各个属性的get，set方法， 数据更新时触发消息给订阅者，实现数据绑定功能。
Object.defineProperty(obj, prop, descriptor)方法直接在一个对象上定义一个新属性，或者修改一个已经存在的属性，并返回这个对象。 该方法接受3个参数：
obj 定义属性的对象。
prop 被定义或修改的属性名。
descriptor 被定义或修改的属性的描述符。
一般情况通过直接给对象属性赋值来创建属性或者修改对应属性，而使用Object.defineProperty可以修改对象属性的一些额外默认配置。 如：
const obj = {name: 'Tom'};
Object.defineProperty(obj, 'name', {
get: function(val) {
return 'Jerry';
}
})
console.log(obj.name);
//输出： JerryObject.defineProperty详细解释，请戳这里
mvvm实现的主要流程：
数据代理，访问实例上的属性时直接返回对应data里的属性
数据监听，对实例上的属性监听，如果数据改变通知订阅者更新
指令解析，对每个元素节点进行解析，替换数据并绑定更新函数
链接数据监听和指令解析，保证每个数据的更新，指令解析都可以获取并更新视图
实例化类：
new MVVM({
el: '#app',
data() {
return {
message: 'hello mvvm'
}
}
})数据代理：
class MVVM {
constructor(options) {
this.$options = options || {};
let data = this._data = this.$options.data();
// 数据代理 vm.xxx => vm._data.xxx
Object.keys(data).forEach(key => {
this._proxyData(key);
});
// observe(data, this);
// this.$compile = new Compile(options.el || document.body, this);
}
_proxyData(key) {
Object.defineProperty(this, key, {
configurable: true,
enumerable: true,
get: () => {
return this._data[key];
},
set: newVal => {
this._data[key] = newVal;
}
});
}
}数据监听，劫持实例属性更新
class Observer {
constructor(data) {
this.data = data;
Object.keys(this.data).forEach(key => {
this.defineReactive(key, this.data[key]);
})
}
// 定义反应
defineReactive(key, val) {
let dep = new Dep();
Object.defineProperty(this.data, key, {
enumerable: true,
configurable: false,
get: () => {
return val;
},
set: newVal => {
if (val === newVal) {
return;
}
val = newVal;
// 赋值对象再进行劫持
observe(val);
... // 数据修改通知
}
})
}
}
function observe(val) {
if (!val || typeof val !== 'object') {
return;
}
return new Observer(val);
}指令解析部分代码
class Compile {
constructor(el, vm) {
this.$vm = vm;
this.$el = this.isElementNode(el) ? el : document.querySelector(el);
if (this.$el) {
this.$fragment = this.node2Fragment(this.$el);
this.init();
this.$el.appendChild(this.$fragment);
}
}
init() {
this.compileElement(this.$fragment);
}
node2Fragment(el) {
let fragment = document.createDocumentFragment(), child;
// 原生节点拷贝到fragment
while (child = el.firstChild) {
// appendChild将元素从dom上移到fragment
fragment.appendChild(child);
}
return fragment;
}
compileElement(el) {
let childNodes = el.childNodes;
[].slice.call(childNodes).forEach(node => {
let text = node.textContent;
let reg = /\{\{(.*)\}\}/;
if (this.isElementNode(node)) {
this.compile(node);
} else if (this.isTextNode(node) && reg.test(text)) {
this.compileText(node, RegExp.$1);
}
if (node.childNodes && node.childNodes.length) {
this.compileElement(node);
}
})
}
}其中
while (child = el.firstChild) {
// appendChild将元素从dom上移到fragment
fragment.appendChild(child);
}通过appendChild改变原dom结构特点，逐步把dom元素节点移到fragment中。
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