實現一個簡單vue

1. 實現一個監聽器Observer，用來劫持並監聽全部屬性，若是有變更的，就通知訂閱者。
2. 實現一個訂閱者Watcher，能夠收到屬性的變化通知並執行相應的函數，從而更新視圖。
3. 實現一個解析器Compile，能夠掃描和解析每一個節點的相關指令，並根據初始化模板數據以及初始化相應的訂閱器。　　

<div id="app">
 <h2>{{title}}</h2>
 <input v-model="name">
 <h1>{{name}}</h1>
 <button v-on:click="clickMe">click me!</buttuon>
</div>

<script type="text/javascript">
 new Vue({
     el: '#app',
     data: {
         title: 'hello world',
         name: 'canfoo'
     },
     methods: {
         clickMe: function () {
             this.title = 'hello world';
         }
     }
 })
</script>

function Vue (options) {
    var self = this;
    this.data = options.data;
    this.methods = options.methods;
    Object.keys(this.data).forEach(function(key) {
        self.proxyKeys(key);
    });
    observe(this.data);
    new Compile(options.el, this);
    options.mounted.call(this);//全部事情處理好後執行mounted函數
}

Vue.prototype = {
    proxyKeys: function(key) {
        var self = this;
        Object.defneProperty(this, key, {
            enumerable: false;
            configurable: true;
            get: function getter () {
                return self.data[key];
            },
            set: function setter (newVal) {
                self.data[key] = newVal;
            }
        })
    }
}

function Observer(data) {
    Object.keys(data).forEach(function(key) {
        defineReactive(data, key, data[key]);
    })
}

function defineReactive(data, key, val) {
    var dep = new Dep();
    Object.defineProperty(data, key, {
        enumerable: true,
        configurable: true,
        get: function getter () {
            if (Dep.target) {
                dep.addSub(Dep.target);
            }
            return val;
        },
        set: function setter (newVal) {
            if (newVal === val) {
                return;
            }
            val = newVal;
            dep.notify();
        }
    })
}

function Dep () {
    this.subs = [];
}

Dep.prototype = {
    addSub: function(sub) {
        this.subs.push(sub);
    },
    notify: function() {
        this.subs.forEach(function(sub) {
            sub.update();
        });
    }
};

Dep.target = null;

function Compile(el, vm) {
    this.vm = vm;
    this.el =  document.querySlector(el);
    this.fragment = null;
    this,init();
}

Compile.prototype = {
    init: function() {
        this.fragment = this.nodeToFragment(this.el);
        this.compileElement(this.fragment);
        this.el.appendChild(this.fragment);
    },
    nodeToFragment: function(el) {
        var fragment = document.createDocumentFragment();
        var child = el.firstChild;
        while (child) {
            //將dom元素移入fragment中
            fragment.appendChild(child);
            child = el.firstChild;
        }
        return fragment;
    },
    compileElement: function(el) {
        var childNodes = el.childNodes;
        var self = this;
        [].slice.call(childNodes).forEach(function(node) {
            var reg = /\{\{(.*)\}\}/;
            var text = node.textContent;
            if (self.isElementNode(node)) {
                self.compile(node);
            } else if (self.isTextNode(node) && reg.test(text)) {
                self.compileText(node, reg.exec(test)[1]);
            }
            if(node.childNodes && node.childNodes.length) {
                self.compileElement(node);
            }
        })
    },
    compile: function(node) {
        var nodeAttrs = node.atrributes;
        var self = this;
        Array.prototype.forEach.call(nodeAttrs, function(attr) {
            var attrName = attr.name;
            if (self.isDirective(attrName)) {
                var exp = attr.value;
                var dir = attrName.substring(2);
                if(self.isEventDirective(dir)) {//事件指令
                    self.compileEvent(node, self.vm, exp, dir);
                }else {//v-model指令
                    self.compileModel(node, self.vm, exp, dir);
                }
                node.removeAttribute(attrName);
            }
        })
    },
    compileEvent: function(node, vm, exp, dir) {
        var eventType = dir.split(':')[1];
        var cb = vm.methods && vm.methods[exp];
        if (eventType && cb) {
            node.addEventListener(eventType, cb.bind(vm), false);
        }
    },
    compileModel: function (node, vm, exp, dir) {
        var self = this;
        var val = this.vm[exp];
        this.modelUpdater(node, val);
        new Watcher(this.vm, exp, function(value) {
            self.modelUpdater(node, value);
        })
        node.addEventListener('input', function(e) {
            var newValue = e.target.value;
            if (val === newValue) {
                return;
            }
            self.vm[exp] = newValue;
            val = newValue;
        })
    }
    compileText: function(node, exp) {
        var self = this;
        var initText = this.vm[exp];
        this.updateText(node, initText);
        new Watcher(this.vm, exp, function(value) {
            self.updateText(node, value);
        })

    },
    modelUpdater: function(node, value, oldValue) {
        node.value = typeof value == 'undefined'?'':value;
    }
    updateText: function(node, value) {
        node.textContent = typeof value == 'undefined'?'':value;
    },
    isDirective: function(attr) {
        return attr.indexOf('v-') == 0;
    },
    isElementNode: function(node) {
        return node.nodeType == 1;
    },
    isTextNode: function(node) {
        return node.nodeType == 3;
    },
    isEventDirective: function(dir) {
        return dir.indexOf('on:') === 0;
    }
}

function Watcher(vm, exp, cb) {
    this.cb = cb;
    this.vm = vm;
    this.exp = exp;
    this.value = this.get();//將本身添加到訂閱器的操做
}

Watcher.prototype = {
    update: function() {
        this.run();
    },
    run: function() {
        var value = this.vm.data[this.exp];
        var oldVal = this.value;
        if (value !== oldVal) {
            this.value = value;
            this.cb.call(this.vm, value, oldVal);
        }
    },
    get: function() {
        Dep.target = this;  // 緩存本身
        var value = this.vm.data[this.exp]  // 強制執行監聽器裏的get函數
        Dep.target = null;  // 釋放本身
        return value;
    }
}