源码如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>代码雨</title>
<style>
* {
margin: 0;
padding: 0;
overflow: hidden;
width: 100%;
height: 100%;
}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<script>
let canvas = document.querySelector('canvas');
let ctx = canvas.getContext('2d');
let width = canvas.width = screen.availHeight;
let height = canvas.height = screen.availWidth;
let str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
let arr = Array(Math.ceil(canvas.width / 10)).fill(0);
const rain = () => {
ctx.fillStyle = 'rgba(0,0,0,0.05)';
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = '#0f0';
ctx.font = '15px Georgia';
ctx.textBaseline = 'top';
arr.forEach((item, index) => {
ctx.fillText(str[Math.floor(Math.random() * str.length)], index * 20, item);
if (item > canvas.height||item> Math.random() * 30000) {
arr[index] = 0;
}
else {
arr[index] += 15;
}
});
};
setInterval(rain, 30);
</script>
</body>
</html>
