本文实例讲述了JavaScript生成的动态下雨背景效果实现方法。分享给大家供大家参考。具体实现方法如下：
<HEAD>
<TITLE>JavaScript生成的动态下雨背景效果</TITLE>
</HEAD>
<BODY bgcolor="#fef4d2" >
<center>
<script language=JavaScript>
<!-- [Step1]: 在此能够设置雨滴的多少 -->
var rainsize = 40;
<!-- [Step2]: 这里可以更改下雨的速度，数值大速度慢 -->
var speed = 10;
var x = new Array();
var y = new Array();
var r = new Array();
var cx = new Array();
var cy = new Array();
var doc_width = document.body.clientWidth;
var doc_height = document.body.clientHeight;
for(i=0; i<rainsize; ++i) {
initRain();
if (i == 0) {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: ");
document.write("absolute; Z-INDEX: "+ i +"; VISIBILITY: ");
document.write("visible; TOP: 15px; LEFT: 15px;\"><font color=\"blue\">");
document.write(",</font></div>"); }
else {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: ");
document.write("absolute; Z-INDEX: "+ i +"; VISIBILITY: ");
document.write("visible; TOP: 15px; LEFT: 15px;\"><font color=\"blue\">");
document.write(",.</font></div>"); }
}
function initRain() {
a = 6;
r[i] = 1;
sn = Math.sin(a);
cs = Math.cos(a);
cx[i] = Math.random() * doc_width + 1;
cy[i] = Math.random() * doc_height + 1;
x[i] = r[i] * sn + cx[i];
y[i] = cy[i];
}
function raindropIE() {
for (i = 0; i < rainsize; ++ i) {
updateRain();
if ((x[i] <= 1) || (x[i] >= (doc_width - 20)) || (y[i] >= (doc_height - 20))) {
makeRain();
doc_width = document.body.clientWidth;
doc_height = document.body.clientHeight; }
document.all["dot"+i].style.pixelTop = y[i];
document.all["dot"+i].style.pixelLeft = x[i]; }
setTimeout("raindropIE()", speed);
}
function updateRain() {
r[i] += 10;
x[i] = r[i] * sn + cx[i];
y[i] = r[i] * cs + cy[i];
}
function makeRain() {
r[i] = 1;
cx[i] = Math.random() * doc_width + 1;
cy[i] = 1;
x[i] = r[i] * sn + cx[i];
y[i] = r[i] * cs + cy[i];
}
raindropIE();
</script>
</BODY>
</HTML>
希望本文所述对大家的javascript程序设计有所帮助。