<template>
    <div>
        <div class="scroll" :class="{show:isActive}">
            <div id="toTop" @click="toTop(step)">&lt;</div>
            <div id="toBottom" @click="toBottom(step)">&gt;</div>
        </div>
    </div>
</template>
<script>
    export default{
        props:{
            step:{   //此数据是控制动画快慢的
                type:Number,
                default:50  
            }
        },
        data(){
            return {
                isActive:false,
            }
        },
        methods:{
            toTop(i){
                //参数i表示间隔的幅度大小，以此来控制速度
                document.documentElement.scrollTop-=i;
                if (document.documentElement.scrollTop>0) {
                    var c=setTimeout(()=>this.toTop(i),16);
                }else {
                    clearTimeout(c);
                }
            },
            toBottom(i){
                var clientHeight=document.documentElement.clientHeight||document.body.clientHeight;
                var scrollHeight=document.documentElement.scrollHeight;
                var height=scrollHeight-clientHeight; //超出窗口上界的值就是底部的scrolTop的值
                document.documentElement.scrollTop+=i;
                if (document.documentElement.scrollTop<height) {
                    var c=setTimeout(()=>this.toBottom(i),16);
                }else {
                    clearTimeout(c);
                }
            }
        },
        created(){
            var vm=this;
            window.onscroll=function(){
                if (document.documentElement.scrollTop>60) {
                    vm.isActive=true;
                }else {
                    vm.isActive=false;
                }
            }
        }
    }
</script>
<style scoped>
    .scroll{
            position: fixed;
            right: 10px;
            bottom: 60px;
            width: 45px;
            height: 90px;
            cursor: pointer;
            display: none;
        }
        .scroll>div{
            width: 45px;
            height: 45px;
            transform: rotate(90deg);
            line-height: 45px;
            text-align: center;
            font-size: 35px;
            font-family: "黑体";
            background-color: rgba(0,0,0,.2);
            color: #fff;
        }
        .scroll>div:hover{
            background-color: rgba(0,0,0,.5);
        }
        .show{
            display: block;
        }
</style>