用js改变backgroundImage属性，在iphone上测试，每次更换图片都会闪一下。

update：
只有iphone会闪，使用了onload也闪，代码如下

  function selection(num0, num1, num2) {
            var img = new Image();
            img.src = urls[num0][1];
            img.onload = function () {
                console.log("complete");
                selections[num0].style.backgroundImage = "url(" + urls[num0][1] + ")";
                list[num0].style.display = "block";
                selections[num1].style.backgroundImage = "url(" + urls[num1][0] + ")";
                list[num1].style.display = "none";
                selections[num2].style.backgroundImage = "url(" + urls[num2][0] + ")";
                list[num2].style.display = "none";
            }
        }