组件全局挂载的问题？ appendChild

有什么方法能替换这种效果嘛？

Vue.prototype.$myLoading = MyLoading

import Vue from 'vue'  
import MyLoading from './MyLoading.vue'  

const MyLoadingBox = Vue.extend(MyLoading)  

MyLoading.open = function(){  
    let instance = new MyLoadingBox().$mount()  
    setTimeout(() => {  
        // let query = uni.createSelectorQuery().in(this);  
        // console.log(query.select('.my-loading'))  

        let dom = document.getElementsByClassName('my-loading')[0]  
        if (dom) {  
            dom.appendChild(instance.$el)  
        } else {  
            document.body.appendChild(instance.$el)  
        }  
    })  
}  
MyLoading.close = function(){  
    let loading = document.getElementsByClassName('Loading-box')[0];  
    loading.remove();  
}  

export default MyLoading