vue自定义组件中报错，提示not defined

directives: {
// 发送消息后滚动到底部
"scroll-bottom"() {
Vue.nextTick(() => {
this.el.scrollTop = this.el.scrollHeight - this.el.clientHeight;
});
}
},

v-scroll-bottom='this'//先用指令绑定全局对象
directives: {
    // 用binding.value获取vue全局对象
    'scroll-bottom': (el,binding,vnode)=>{
        console.log(el,binding,vnode)
        const This = binding.value;
        This.$nextTick(() => {
            el.scrollTop = el.scrollHeight - el.clientHeight;
        });
    }
}