用js来控制，几张图片，一直循环过渡性切换，

用js来控制，几张图片，一直循环过渡性切换，
   var bgs = ["images/index/sp-body-center-img2.jpg", "images/index/sp-body-center-img3.jpg", "images/index/sp-body-center-img5.jpg", "images/index/sp-body-center-img.jpg"];
      var curbg = -1;
      window.onload = function () {
          setInterval(function () {
              document.getElementById("bodyHeadTop").style.background = "url('" + bgs[curbg >= bgs.length - 1 ? curbg = 0 : ++curbg] + "')  no-repeat center top #1559bf";
              $("#bodyHeadTop").css({ "-webkit-transition": "1.2s", "-moz-transition": "1.2s", "t-ms-ransition": "1.2s", "-o-transition": "1.2s", "transition": "1.2s" });
          }, 5500);

      };

一般使用时，在div先设置好一个北背景图，然后