剖析 Vue 原理 & 实现双向绑定 MVVM

<div id="mvvm-app">    <input type="text" v-model="word">    <p>{{word}}</p>    <button v-on:click="sayHi">change model</button></div><script src="./js/observer.js"></script><script src="./js/watcher.js"></script><script src="./js/compile.js"></script><script src="./js/mvvm.js"></script><script>    var vm = new MVVM({        el: '#mvvm-app',        data: {            word: 'Hello World!'        },        methods: {            sayHi: function() {                this.word = 'Hi, everybody!';            }        }    });</script>

var data = {name: 'kindeng'};observe(data);data.name = 'dmq'; // 哈哈哈，监听到值变化了 kindeng --> dmq
function observe(data) {        if (!data || typeof data !== 'object') {                return;    }        // 取出所有属性遍历    Object.keys(data).forEach(function(key) {        defineReactive(data, key, data[key]);    });};
function defineReactive(data, key, val) {    observe(val); // 监听子属性    Object.defineProperty(data, key, {        enumerable: true, // 可枚举        configurable: false, // 不能再define        get: function() {                        return val;        },        set: function(newVal) {                        console.log('哈哈哈，监听到值变化了 ', val, ' --> ', newVal);            val = newVal;        }    });}

// ... 省略function defineReactive(data, key, val) {        var dep = new Dep();    observe(val); // 监听子属性
    Object.defineProperty(data, key, {                // ... 省略        set: function(newVal) {                        if (val === newVal) return;                        console.log('哈哈哈，监听到值变化了 ', val, ' --> ', newVal);            val = newVal;            dep.notify(); // 通知所有订阅者        }    });}            function Dep() {        this.subs = [];}Dep.prototype = {    addSub: function(sub) {                this.subs.push(sub);    },    notify: function() {                this.subs.forEach(function(sub) {            sub.update();        });    }};

// Observer.js// ...省略
Object.defineProperty(data, key, {    get: function() {                // 由于需要在闭包内添加watcher        // 所以通过Dep定义一个全局target属性，暂存watcher, 添加完移除        Dep.target && dep.addDep(Dep.target);                return val;    }        // ... 省略});    // Watcher.jsWatcher.prototype = {    get: function(key) {        Dep.target = this;           // 这里会触发属性的getter，从而添加订阅者             this.value = data[key];         Dep.target = null;    }}

function Compile(el) {        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);    }}Compile.prototype = {    init: function() { this.compileElement(this.$fragment); },    node2Fragment: function(el) {         var fragment = document.createDocumentFragment(), child;        // 将原生节点拷贝到fragment        while (child = el.firstChild) {            fragment.appendChild(child);        }                return fragment;    }};

Compile.prototype = {    // ... 省略    compileElement: function(el) {        var childNodes = el.childNodes, me = this;        [].slice.call(childNodes).forEach(function(node) {            var text = node.textContent;            var reg = /\{\{(.*)\}\}/;    // 表达式文本            // 按元素节点方式编译            if (me.isElementNode(node)) {                me.compile(node);            } else if (me.isTextNode(node) && reg.test(text)) {                me.compileText(node, RegExp.$1);            }             // 遍历编译子节点            if (node.childNodes && node.childNodes.length) {                me.compileElement(node);            }        });    },
    compile: function(node) {        var nodeAttrs = node.attributes, me = this;        [].slice.call(nodeAttrs).forEach(function(attr)             // 规定：指令以 v-xxx 命名            // 如 <span v-text="content"></span> 中指令为 v-text            var attrName = attr.name;    // v-text            if (me.isDirective(attrName)) {                var exp = attr.value; // content                var dir = attrName.substring(2);    // text                if (me.isEventDirective(dir)) {                    // 事件指令, 如 v-on:click                    compileUtil.eventHandler(node, me.$vm, exp, dir);                } else {                    // 普通指令                    compileUtil[](node, me.$vm, exp);                }            }        });    }}; // 指令处理集合var compileUtil = {    text: function(node, vm, exp) {        this.bind(node, vm, exp, 'text');    },    bind: function(node, vm, exp, dir) {        var updaterFn = updater[dir + 'Updater'];        // 第一次初始化视图        updaterFn && updaterFn(node, vm[exp]);        // 实例化订阅者，此操作会在对应的属性消息订阅器中添加了该订阅者watcher        new Watcher(vm, exp, function(value, oldValue) {            // 一旦属性值有变化，会收到通知执行此更新函数，更新视图            updaterFn && updaterFn(node, value, oldValue);        });    }};            // 更新函数var updater = {    textUpdater: function(node, value) {        node.textContent = typeof value == 'undefined' ? '' : value;    }};

function Watcher(vm, exp, cb) {    this.cb = cb;    this.vm = vm;    this.exp = exp;    // 此处为了触发属性的getter，从而在dep添加自己，结合Observer更易理解    this.value = this.get(); }Watcher.prototype = {    update: function() {        this.run();    // 属性值变化收到通知    },    run: function() {        var value = this.get(); // 取到最新值        var oldVal = this.value;        if (value !== oldVal) {            this.value = value;            // 执行Compile中绑定的回调，更新视图            this.cb.call(this.vm, value, oldVal);         }    },    get: function() {        Dep.target = this;    // 将当前订阅者指向自己        var value = this.vm[exp];    // 触发getter，添加自己到属性订阅器中        Dep.target = null;    // 添加完毕，重置        return value;    }};// 这里再次列出Observer和Dep，方便理解Object.defineProperty(data, key, {    get: function() {        // 由于需要在闭包内添加watcher        // 所以可以在Dep定义一个全局target属性，暂存watcher, 添加完移除        Dep.target && dep.addDep(Dep.target);        return val;    }    // ... 省略});Dep.prototype = {    notify: function() {        this.subs.forEach(function(sub) {            sub.update(); // 调用订阅者的update方法，通知变化        });    }};

function MVVM(options) {    this.$options = options;    var data = this._data = this.$options.data;    observe(data, this);    this.$compile = new Compile(options.el || document.body, this);}

var vm = new MVVM({data:{name: 'kindeng'}}); vm._data.name = 'dmq';

var vm = new MVVM({data: {name: 'kindeng'}}); vm.name = 'dmq';

function MVVM(options) {    this.$options = options;    var data = this._data = this.$options.data, me = this;    // 属性代理，实现 vm.xxx -> vm._data.xxx    Object.keys(data).forEach(function(key) {        me._proxy(key);    });    observe(data, this);    this.$compile = new Compile(options.el || document.body, this);}
MVVM.prototype = {    _proxy: function(key) {        var me = this;        Object.defineProperty(me, key, {            configurable: false,            enumerable: true,            get: function proxyGetter() {                return me._data[key];            },            set: function proxySetter(newVal) {                me._data[key] = newVal;            }        });    }};