<script>
export default {
    data() {
        return {
            msg: 'hello'
        }
    },
    watch: {
        // 简单监听
        msg(newVal, oldVal) {
            console.log(newVal, oldVal)
        },
        // 深度监听
        msg: {
            deep: true,
            immediate: true,
            handler(newVal, oldVal) {
                console.log(newVal, oldVal)
            }
        }
    },
    created() {
        // 函数式监听
        const watcher = this.$watch('msg', (newVal, oldVal) => {
            console.log(newVal, oldVal)
        }, {
            deep: true,
            immediate: true
        })
        // 取消监听
        watcher()
    }

}
</script>