<template>
 <div class="vue-scroll" ref="vueScrollW">
 <div class="vue-scroll-w" ref="vueScroll" >
 <div class="vue-scroll-c" :style="{width:cWidth}">
 <slot></slot>
 </div>
 </div>
 <div class="vue-scrollbar" v-if="rate < 1">
 <div class="vue-scrollbar-thumb"
 :style="{height:thumbH,top:thumbTop}"
 @mousedown="onmousedown"
 @mouseup="onmouseup"
 ></div>
 </div>
 </div>
</template>
 
<script>
 
 
 
export default {
 name:"vue-scroll",
 data(){
 return {
 thumb:0,
 top:0,
 rate:2,
 moveTop:null,
 isDrag:false,
 cw:10,
 observer:null
 }
 },
 computed:{
 thumbH(){
 return this.thumb + "px";
 },
 thumbTop(){
 return this.top + "px";
 },
 cWidth(){
 return this.cw + "%";
 }
 
 },
 updated(){
 if(!window.MutationObserver){
 this.refresh();
 }
 },
 mounted(){
 var me = this;
 me.$refs.vueScroll.addEventListener("scroll",me.onscroll.bind(me));
 window.addEventListener("mouseup",me.onmouseup.bind(me));
 window.addEventListener("mousemove",me.onmousemove.bind(me));
 
 if(window.MutationObserver){
 //MutationObserver 最低只兼容 ie11
 me.observer = new window.MutationObserver(me.mutationCallback.bind(me));
 me.observer.observe(me.$refs.vueScroll, {
 attributes: true,
 childList: true,
 subtree: true
 });
 }
 
 me.refresh();
 },
 methods:{
 mutationCallback(mutationsList){
 this.refresh();
 },
 onscroll(){
 this.top = this.$refs.vueScroll.scrollTop * this.rate; //計算滾動條所在的高度
 if(this.rate < 1){
 this.eventTrigger(this.top);
 }
 },
 refresh(){
 var me = this;
 var vueScroll = me.$refs.vueScroll;
 var rate = vueScroll.clientHeight / vueScroll.scrollHeight; //滾動條高度的比例,也是滾動條top位置的比例
 me.rate = rate;
 if(rate < 1){
 //需要出現滾動條,并計算滾動條的高度
 me.thumb = rate * vueScroll.clientHeight; //滾動條的 bar 的高度
 //計算出原生的滾動條的寬度
 var w = me.$refs.vueScrollW.clientWidth;
 //根據比例，轉換為內容的百分比
 me.cw = w/vueScroll.clientWidth *100;
 }else{
 //不需要出現滾動條
 me.thumb = 0;
 me.cw = 10;
 }
 },
 
 onmousedown(){
 this.isDrag = true;
 this.moveTop = null;
 },
 onmouseup(){
 this.isDrag = false;
 },
 onmousemove(e){
 if(this.isDrag){
 if(this.moveTop !== null){
 var speed = e.screenY - this.moveTop;
 var top = this.top + speed;
 this.scrollThumb(top);
 }
 this.moveTop = e.screenY;
 e.preventDefault();
 }
 
 },
 scrollThumb(top){
 if(top < 0 ){
 top = 0;
 
 }
 if(top > this.$refs.vueScroll.clientHeight-this.thumb){
 top = this.$refs.vueScroll.clientHeight-this.thumb;
 
 }
 
 this.$refs.vueScroll.scrollTop = top/this.rate;
 this.top = top;
 },
 eventTrigger(top){
 if(top === 0){
 this.$emit("reachTop"); //到達頂部
 }
 if(top === this.$refs.vueScroll.clientHeight-this.thumb){
 this.$emit("reachBottom"); //到達底部與
 }
 this.$emit("vuescroll",this.$refs.vueScroll.scrollTop,this.top);//返回內容滾動的高度 和 滾動條所在的高度
 },
 scrollTo(scrollTop){
 //對外的api，滾動的內容的哪里
 this.$refs.vueScroll.scrollTop = scrollTop;
 this.$nextTick(()=>{
 this.onscroll();
 })
 }
 },
 destroyed(){
 var me = this;
 me.$refs.vueScroll && me.$refs.vueScroll.removeEventListener("scroll",me.onscroll.bind(me));
 window.removeEventListener("mouseup",me.onmouseup.bind(me));
 window.removeEventListener("mousemove",me.onmousemove.bind(me));
 me.observer&&me.observer.disconnect();
 }
}
</script>
 
<style lang="scss" scoped>
.vue-scroll{
 height: 100%;
 width: 100%;
 overflow: hidden;
 position: relative;
 .vue-scroll-w{
 width: 1000%;
 height: 100%;
 overflow: auto;
 .vue-scroll-c{
 position: relative;
 width: 10%;
 }
 }
 .vue-scrollbar{
 position: absolute;
 z-index: 1;
 right: 0;
 top: 0;
 width: 4px;
 height: 100%;
 background: #EEEEEE;
 opacity: 0.6;
 .vue-scrollbar-thumb{
 position: absolute;
 top: 0;
 right: 0;
 width: 4px;
 border-radius: 4px;
 background: #D3D3D3;
 &:hover{
 background: #bbb;
 }
 &:active{
 background: #aaa;
 }
 }
 }
}
</style>

<template>
 <div class="scroll">
 <vueScroll>
 <ul>
 <li v-for="item in 60" :key="item">{{item}}</li>
 </ul>
 </vueScroll>
 </div>
</template>
 
<script>
import vueScroll from "@/components/vue-scroll.vue"
export default {
 data(){
 return {
 count:60
 }
 },
 components:{
 vueScroll
 },
 mounted(){
 
 }
}
</script>
<style lang="less" scoped>
.scroll{
 width: 400px;
 height: 600px;
 margin: 0 auto;
 border: 1px solid red;
 ul{
 li{
 line-height: 30px;
 border-bottom: 1px solid #ddd;
 }
 }
}
</style>