自己编写的焦点图片代码
适合初学者学习
var swapTime = 5000;
var picC = 0;
function $(id){return document.getElementById(id)}
var p=$("pic").getElementsByTagName("li");
var bt=$("b").getElementsByTagName("li");
var title=$("tit").getElementsByTagName("li");
var rbtn = document.getElementById("bt_r");
var lbtn = document.getElementById("bt_l");
var j=bt.length;