图片预加载

function loadImage(url, callback) {

    if(url!='null') {

        var img = new Image();

        img.src = url;

        if(img.complete) {

            callback(img);

        } else {

            img.onload = function(){

                img.onload = null;

                callback(img);

            } 

        }

    } 

}



loadImage(pic_url,loadImage);