그림의 위쪽과 아래쪽을 전환합니다

<html lang="zh-cn">
<head>
    <meta charset="UTF-8">
    <title> title>
head>
<body>
    <img src="images/001.jpg" id="imgid"><br/>
    <input type="button" value=" " id="prev">
    <input type="button" value=" " id="next">

<script>
    var adimg=['images/001.jpg','images/002.jpg','images/003.jpg'];
    var numimg=0;
    window.onload=function(){
        document.getElementById('prev').onclick=prevProcess;
        document.getElementById('next').onclick=nextProcess;
    }
    function prevProcess(){
        if(numimg==0){
            numimg=adimg.length;
        }
        numimg--;
        document.getElementById('imgid').src=adimg[numimg];
        return false;
    }
    function nextProcess(){
        numimg++;
        if(numimg==adimg.length){
            numimg=0;
        }

        document.getElementById('imgid').src=adimg[numimg];
        return false;
    }
script>
body>
html>