javascript实现点击图片切换

<div class="img">
 <img src="images/1.jpg" id="myimg" class="myimg" alt="这里是1.jpg">
 <p>
 <input type="button" id="pre" class="btn" value="上一张">
 <input type="button" id="next" class="btn" value="下一张">
 </p> 
</div>

*{
 margin: 0;
 padding: 0;
}
img{
 boder:none;
}
button{
 outline: none;
 vertical-align: middle;
}
.img{
 width: 100%;
 margin-left: auto;
 margin-right: auto;
 margin-top: 20px;
 text-align: center;
}
.myimg{
 width: 500px;
 height: 300px;
}
p{
 text-align: center;
}
p .btn{
 width: 100px;
 height: 30px;
 background: #306bbf;
 color: #fff;
 margin-top: 20px;
 margin-bottom: 20px;
}

//找标签
let myimg = document.getelementbyid("myimg");
let pre=document.getelementbyid("pre");
let next=document.getelementbyid("next");

//创建一个保存图片的数组
let arrimg = ["images/1.jpg", "images/1-1.png", "images/3.jpg" ];
//数组的索引下标
let index=0;
//定义事件函数
function preimg(event){
 index--;
 //实现循环切换
 if (index<0)
 {
  index=arrimg.length-1;
 }
 myimg.src = arrimg[index];
}
function nextimg(event){
 index++;
 //实现循环切换
 if (index>arrimg.length-1)
 {
 index=0;
 }
 myimg.src = arrimg[index];
}

pre.addeventlistener('click',preimg);
next.addeventlistener('click',nextimg);