源代码 ：
点击运行
<!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"> <p style = "font-size:25px;">计数器: {{ counter }}</p> <button @click = "counter++" style = "font-size:25px;">点我</button> </div> <script> const app = { data() { return { counter: 1 } } } vm = Vue.createApp(app).mount('#app') vm.$watch('counter', function(nval, oval) { alert('计数器值的变化 :' + oval + ' 变为 ' + nval + '!'); }); </script> </body> </html>
运行结果