<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>飞翔的小球</title>
<style>
*{
margin: 0;
padding: 0;
}
#ball{
width: 200px;
height: 200px;
border-radius: 50%;
background: pink;
position: absolute;
}
</style>
</head>
<body>
<div id="ball"></div>
</body>
<script>
//获取元素
var ball = document.getElementById('ball');
//封装随机函数
function rand(m,n){
return Math.floor(Math.random() * (n - m + 1)) + m;
}
//封装改变颜色的函数
function changeBg(){
var r = rand(0,255);
var g = rand(0,255);
var b = rand(0,255);
ball.style.background = 'rgb('+ r +','+ g +','+ b +')';
}
changeBg();
//设置小球运动步径
var stepX = 2;
var stepY = 2;
setInterval(function(){
var newLeft = ball.offsetLeft + stepX;
var newTop = ball.offsetTop + stepY;
var clientWidth = document.documentElement.clientWidth || document.body.clientWidth;
var clientHeight = document.documentElement.clientHeight || document.body.clientHeight;
if(newLeft >= clientWidth - ball.offsetWidth){
stepX *= -1;
changeBg();
}
if(newLeft <= 0){
stepX *= -1;
changeBg();
}
if(newTop >= clientHeight - ball.offsetHeight){
stepY *= -1;
changeBg();
}
if(newTop <= 0){
stepY *= -1;
changeBg();
}
ball.style.left = newLeft + 'px';
ball.style.top = newTop + 'px';
},20);
</script>
</html>