源代码 ：
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Vue 测试实例 - 开源教程(ossoft.cn)</title> <script src="https://unpkg.com/vue@next"></script> </head> <body> <div id = "app"> 千米 : <input type = "text" v-model = "kilometers"> 米 : <input type = "text" v-model = "meters"> </div> <p id="info"></p> <script> const app = { data() { return { kilometers : 0, meters:0 } }, watch : { kilometers:function(val) { this.kilometers = val; this.meters = this.kilometers * 1000 }, meters : function (val) { this.kilometers = val/ 1000; this.meters = val; } } } vm = Vue.createApp(app).mount('#app') vm.$watch('kilometers', function (newValue, oldValue) { // 这个回调将在 vm.kilometers 改变后调用 document.getElementById ("info").innerHTML = "修改前值为: " + oldValue + "，修改后值为: " + newValue; }) </script> </body> </html>
运行结果