图片预加载

　　　　　function loadImages(sources, callback) {
            var loadedImages = 0;
            var numImages = 0;
            var images = [];
            numImages = sources.length;
            for(var i = 0, len = sources.length; i < len; i++) {
                images[i] = new Image();
                //当一张图片加载完成时执行
                images[i].onload = function() {
                    //当所有图片加载完成时，执行回调函数callback
                    if(++loadedImages >= numImages) {
                        callback();
                    }
                };
                //把sources中的图片信息导入images数组
                images[i].src = sources[i];
                console.log(images);
            }
        }
        var sources = [
            "./images/answer_bg.jpg",
            "./images/answer_font_bg.png",
            "./images/answer_font1.png",
            "./images/answer_font2.png",
            "./images/answer_font3.png"
        ];
        //执行图片预加载，加载完成后执行main
        loadImages(sources, function() {
            $('#loading').fadeOut();
        });