<div  style="position: absolute;z-index: 10px;">
        <input type="file" id="getfileinput">
        <div>¼ͼƬλã</div>
    </div>
    <div id="checkimg" style="position: relative;top:50px;height: 900px;width:450px;overflow: hidden;background-size: contain;background-repeat:no-repeat;background-position: 0 -200px;">
        <img style="position: absolute;left:0;top:-200px;mix-blend-mode: screen;" src="" width="450">
    </div>
    <script type="text/javascript">
    var obj = document.querySelector('#checkimg'),
        oimg = obj.querySelector('img'),
        bgposy = -200;
    // ͼƬ
    document.querySelector('#getfileinput').addEventListener('change',function(){
        // console.log('change');
        var that = this,filereader;
        if(that.files.length>0){
            filereader = new FileReader();
            filereader.onload = function(e){
                oimg.src=this.result;
                obj.style.backgroundImage='url('+this.result+')';
                oimg.style.top = (bgposy+3)+"px";
            };
            filereader.readAsDataURL(that.files[0]);
  
        }
    },false);
  
    // 
    document.addEventListener('keydown',function(e){
        e.stopPropagation();
        switch(e.keyCode){
            case 38: //
                ++bgposy;
            break;
            case 40: //
                bgposy = bgposy =0?0:--bgposy;
            break;
        }
        console.log(bgposy);
        oimg.style.top = bgposy+"px";
    },false);
  
</script>
