• 官方文档：https://cn.vuejs.org/v2/api/#vm-mount
• 仿写 elementUI的 this.$message。

1. MyNotice/MyNotice.vue

<template>
    <div class="notice-box">
        <div class="message" 
            :class="item.type" 
            v-for="item in msgList" 
            :key="item._name"
        >
            <div class="content">{{item.content}}</div>
        </div>
    </div>
</template>

<script>
const DefaultOption = {
    duration: 1500,
    type: "normal",
    content: "提示内容！",
};
let idx = 0;
export default {
    data() {
        return {
            msgList: [],
        };
    },
    methods: {
        add(msgOpt = {}) {
            // name标识 用于移除弹窗
            let _name = this.getName();
            // 并入默认配置，并赋值
            msgOpt = Object.assign(
                {
                    _name,
                },
                DefaultOption,
                msgOpt
            );
            this.msgList.push(msgOpt);

            setTimeout(() => {
                this.removeMsg(_name);
            }, msgOpt.duration);
        },
        getName() {
            return "msg_" + idx++;
        },
        removeMsg(_name) {
            let index = this.msgList.findIndex((item) => item._name === _name);
            this.msgList.splice(index, 1);
        },
    },
};
</script>

<style lang='scss' scoped>
.notice-box {
    position: fixed;
    top: 50px;
    left: 50%;
    display: flex;
    flex-direction: column;
    align-items: center;
    transform: translateX(-50%);

    .message {
        border-width: 3px;
        min-width: 240px;
        max-width: 500px;
        margin-bottom: 10px;
        border-radius: 3px;
        box-shadow: 0 0 8px #ddd;
        overflow: hidden;

        &.normal {
            border-left: 3px solid #909399;
            background: #f4f4f5;
        }
        &.success {
            border-left: 3px solid #67c23a;
            background: #f0f9eb;
        }
        &.error {
            border-left: 3px solid #f56c6c;
            background: #fef0f0;
        }
        &.warning {
            border-left: 3px solid #e6a23c;
            background: #fdf6ec;
        }

        .content {
            padding: 8px;
            line-height: 1.3;
        }
    }
}
</style>

2. MyNotice/index.js

import Vue from 'vue'
import MyNotice from './MyNotice.vue'

let noticInstance = null,
    NoticeConstructor = Vue.extend(MyNotice),
    init = () => {
        noticInstance = new NoticeConstructor()
        noticInstance.$mount()
        document.body.appendChild(noticInstance.$el)
    },
    caller = (opt) => {
        if (!noticInstance) {
            init()
        }
        noticInstance.add(opt)
    }

export default {
    // 返回 install 函数 用于 Vue.use 注册
    install(vue) {
        vue.prototype.$notice = caller
    },
}

3. main.js

import MyNotice from '@/components/MyNotice/index.js'

Vue.use(MyNotice)

4. 调用

 myNotice() {
    this.$notice({
        type: "success",
        content: "成功信息提示",
        duration: 2000,
    })
 }