写了一个移动小球碰撞边框的练习题，本来以为很简单，结果在细节上卡了几个小时，目前问题是想让小球在途中随机变向，不知道怎么实现。
<html> <head> <style type="text/css"> #box{ width:500px; height:500px; border: 1px solid red; position: relative; } #q{ position:absolute; width: 50px; height: 50px; background: red; border-radius:50%; box-shadow: 1px 1px 1px gray; } </style> </head> <body> <div id="box"> <div id="q"></div> </div> <script language="javascript"> var k1=Math.random()*5, k2=Math.random()*5, a=0, b=0; function move () { a=a+k1; b=b+k2; if (a<=0||a>500-50) {k1=-k1}; if (b<=0||b>500-50) {k2=-k2}; q.style.left = a + "px"; q.style.top = b + "px"; setTimeout(‘move()‘,10); } move() </script> </body> </html>
原文：http://www.cnblogs.com/Amarantine/p/4942304.html