//给mask添加事件，让其随着鼠标移动
superMask.onmousemove=function(){
var left=event.offsetX-175/2;
left=left>0?left:0;
left=left<175?left:175;
var top=event.offsetY-175/2;
top=top>0?top:0;
top=top<175?top:175;
mask.style.left=left+"px";
mask.style.top=top+"px";
//控制大图的预览区
largeDiv.style.backgroundPositionX=left*2*(-1)+'px';
largeDiv.style.backgroundPositionY=top*2*(-1)+'px';
}
superMask.onmouseover=function(){
mask.style.display="block";//控制小遮罩显示
largeDiv.style.display="block";//控制大图区显示
var mediumSrc=document.getElementById("mediumImg").src;
var dotIndex=mediumSrc.lastIndexOf(".");
var largeSrc=mediumSrc.substring(0,dotIndex-1)+"l"+mediumSrc.substring(dotIndex);
//console.log(largeSrc);
largeDiv.style.background='url('+largeSrc+')';//大图链接字符串
}
superMask.onmouseout=function(){
mask.style.display="none";
largeDiv.style.display="none";
}