如何实现两个input框的同步更新

 class MVVM {
     constructor(options) {
         this.$options = options;
         this.$el = options.el;
         this.$data = options.data;
         this.observe(this.$data);
         new Compile(this);
     }
     observe(data) {
         if (!data || typeof data !== 'object') {
             return;
         }
         Object.keys(data).forEach(key => {
             this.defineReactive(data, key, data[key]);
         })
     }
     defineReactive(data, key, value) {
         let dep = new Dep();
         Object.defineProperty(data, key, {
             configurable: false,
             enumerable: true,
             get: () => {
                 Dep.target && dep.add(Dep.target);
                 return value;
             },
             set: (newVal) => {
                 if (newVal === value) { return; }
                 value = newVal;
                 dep.notify();
             }
         })
     }
 }
 class Dep {
     constructor() {
         this.deps = [];
     }
     add(dep) {
         this.deps.push(dep);
     }
     notify() {
         this.deps.forEach(dep => {
             dep.update();
         })
     }
 }
 class Watcher {
     constructor(vm, cb) {
         this.vm = vm;
         this.cb = cb;
         Dep.target = this;
         this.vm.$data['word'];
         Dep.target = null;
     }
     update() {
         this.cb.call(this.vm, this.vm.$data['word']);
     }
 }
 class Compile {
     constructor(vm) {
         this.vm = vm;
         this.changeInputValue(vm);
     }
     changeInputValue(vm) {
         let inputs = document.querySelectorAll('input');
         Array.from(inputs).forEach(input => {
             this.update(input,vm);
             input.addEventListener('input', (e) => {
                 vm.$data['word'] = e.target.value;
             }, false)
         })
     }
     update(input,vm) {
         input.value = vm.$data['word'];
         new Watcher(vm, function (value) {
             input.value = value;
         })
     }
 }