console 命令行工具 X clear
console
<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js">

</script>

<body>
    <section id="app">
        {{message}}
    </section>
</body>
<script>
new Vue({
    el: '#app',
    data: {
        message: '页面加载于 ' + new Date().toLocaleString()
    },
    created(){
        // error
        const unWatcher = this.$watch(()=>this.message,()=>{
            if(unWatcher){
                console.log(unWatcher)
            }
        },{immediate:true})

        // success - var
        // var unWatcher = this.$watch(()=>this.message,()=>{
        //     if(unWatcher){
        //         console.log(unWatcher)
        //     }
        // },{immediate:true})
    },
})
</script>