1 <!DOCTYPE html>
2 <html>
3 <head>
4 <meta charset="UTF-8">
5 <title></title>
6 <style type="text/css">
7 *{
8 padding: 0;
9 margin: 0;
10 }
11 #box{
12 width: 500px;
13 height: 400px;
14 border: 1px solid gainsboro;
15 margin: 20px auto 0;
16 position: relative;
17 }
18 #ball{
19 width: 30px;
20 height: 30px;
21 border-radius: 50%;
22 background: red;
23 position: absolute;
24 }
25 </style>
26 </head>
27 <body>
28 <div id="box">
29 <div id="ball"></div>
30 </div>
31 </body>
32 <script type="text/javascript">
33 // 获取 box 和 ball
34 var box = document.getElementById("box");
35 var ball = document.getElementById("ball");
36 var speedX = 0;
37 // 获取小球的初始 left
38 var originLeft = ball.offsetLeft;
39 // ball 最大的移动宽度
40 var maxWidth = box.clientWidth - ball.offsetWidth;
41 // ball 可以移动的最大高度
42 var maxheight = box.clientHeight - ball.offsetHeight;
43 // 定义一个增量(x)
44 var add = 5;
45 // 定义纵向的移动记录值
46 var speedY = 0;
47 // 定义增量2(Y)
48 var dda = 10;
49 // 获取小球的初始 top
50 var originTop = ball.offsetTop;
51
52 setInterval(function(){
53 speedX += add;
54 speedY += dda;
55
56 // 调整 ball 的 left 让他向右移动
57 if(speedX >= maxWidth){
58 add = -add;
59 }
60
61 if(speedX <= 0){
62 add = -add;
63 }
64
65 if(speedY >= maxheight){
66 dda = -dda;
67 }
68 if(speedY <= 0){
69 dda = -dda;
70 }
71
72 ball.style.left = originLeft + speedX + "px";
73 ball.style.top = originTop + speedY + "px";
74
75 },30);
76 </script>
77 </html>
