基于javascript实现图片切换效果

*{
  margin: 0;
  padding: 0;
}
.box{
  width: 800px;
  height: 400px;
  margin: 20px auto;
  position: relative;
  overflow: hidden;
}
.img_box{
  height: 400px;
  width: 3200px;
  position: absolute;
  -moz-transition: 0.5s;
  -webkit-transition: 0.5s;
}
img{
  width: 800px;
  height: 400px;
  float: left;
}
.switch{
  width: 200px;
  height: 100%;
  position: absolute;

}
#left{
  left: 0px;
  top: 0px;
  background: -moz-linear-gradient(left, rgba(84, 84, 84, 0.50), rgba(20%,20%,20%,0));
  background: -webkit-linear-gradient(left, rgba(84, 84, 84, 0.50), rgba(20%,20%,20%,0));
}
#right{
  right:0px;
  top: 0px;
  background: -moz-linear-gradient(left, rgba(20%,20%,20%,0), rgba(84, 84, 84,0.5));
  background: -webkit-linear-gradient(left, rgba(20%,20%,20%,0), rgba(84, 84, 84,0.5));
}
#left:hover{
  background: -moz-linear-gradient(left, rgba(0, 0, 0,0.5), rgba(20%,20%,20%,0));
  background: -webkit-linear-gradient(left, rgba(0, 0, 0,0.5), rgba(20%,20%,20%,0));
}
#right:hover{
  background: -moz-linear-gradient(left, rgba(20%,20%,20%,0), rgba(0, 0, 0,0.5));
  background: -webkit-linear-gradient(left, rgba(20%,20%,20%,0), rgba(0, 0, 0,0.5));
}

var box;
var count=1;
window.Onload=function(){
  box=document.getElementById("img_box");
  var left=document.getElementById("left");
  var right=document.getElementById("right");
  left.addEventListener("click",_left);
  right.addEventListener("click",_right);
  document.body.addEventListener("mouseover",demo);
}
function _right(){
  var dis=0;
  if(count<4){
    dis=count*800;
  }else{
    dis=0;
    count=0;
  }
  box.style.left="-"+dis+"px";
  count+=1;
}
function _left(event){
  var dis=0;
  if(count>1){
    dis=(2-count)*800;
  }else{
    dis=-3*800;
    count=5;
  }
  box.style.left=dis+"px";
  count-=1;
}