放大镜效果

var smallWrap=document.getElementById(‘smallWrap‘);
var swWidth=smallWrap.clientWidth;
var swHeight=smallWrap.clientHeight;
var bigWrap=document.getElementById(‘bigWrap‘);
var ratio=2.28;

smallWrap.onmouseover=function(event){
    var magnifier=document.createElement(‘div‘);
    magnifier.id=‘magnifier‘;
    smallWrap.appendChild(magnifier);       
    setPos(event);
}
smallWrap.onmousemove=function(event){
    setPos(event);   
}
smallWrap.onmouseout=function(){
    smallWrap.removeChild(magnifier);
    bigWrap.style.display=‘none‘;
}

function setPos(event){
    var width=magnifier.clientWidth;
    var height=magnifier.clientHeight;
    var pos=getPosInElem(event,smallWrap);
    var left=pos.x-width/2;
    var top=pos.y-height/2;
    if(left<0){left=0;}
    if(left+width>swWidth){left=swWidth-width;}         
    if(top<0){top=0;}
    if(top+height>swHeight){top=swHeight-height;}
    magnifier.style.left=left+‘px‘;
    magnifier.style.top=top+‘px‘;
    bigWrap.style.display=‘block‘;
    bigWrap.style.backgroundPosition=-left*ratio+‘px‘+‘ ‘+-top*ratio+‘px‘;
    console.log(left+‘--‘+top);
}

function getPosInElem(event,elem){
    return {
        x:event.clientX-elem.getBoundingClientRect().left,
        y:event.clientY-elem.getBoundingClientRect().top
    }
}