1 (function () {
2 // 添加事件监听器
3 function addEvent(a, b, c) {
4 if (a.addEventListener) a.addEventListener(b, c, false);
5 else a.attachEvent && a.attachEvent("on" + b, c)
6 }
7 // 向window.onload添加执行函数
8 function addToOnLoad(a) {
9 if (typeof window.onload != "function") window.onload = a;
10 else {
11 var b = window.onload;
12 window.onload = function () {
13 b();
14 a()
15 }
16 }
17 }
18 // scroll top ,left
19 function getScrollDis() {
20 var scroll = {};
21 for (var type in {
22 Top: "",
23 Left: ""
24 }) {
25 var b = type == "Top" ? "Y" : "X";
26 if (typeof window["page" + b + "Offset"] != "undefined") scroll[type.toLowerCase()] = window["page" + b + "Offset"];
27 else {
28 // <html>
29 b = document.documentElement.clientHeight ? document.documentElement : document.body;
30 scroll[type.toLowerCase()] = b["scroll" + type]
31 }
32 }
33 return scroll;
34 }
35
36 // 获取浏览器窗口高度(不包括工具栏/滚动条)
37 function getWinHeight() {
38
39 var height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
40 return height;
41 }
42
43 //构造函数 ，模拟雪花类
44 function SnowDot(a) {
45 this.parent = document.body;
46 this.createEl(this.parent, a);
47 this.size = Math.random() * 5 + 5; // 随机设置雪花的大小
48 this.el.style.width = Math.round(this.size) + "px";
49 this.el.style.height = Math.round(this.size) + "px";
50 this.maxLeft = document.body.offsetWidth - this.size;
51 this.maxTop = document.body.offsetHeight - this.size;
52 this.left = Math.random() * this.maxLeft;
53 this.top = getScrollDis().top + 1;
54 this.angle = 1.4 + 0.2 * Math.random();
55 // PI/2 =1.57
56 this.minAngle = 1.4;
57 this.maxAngle = 1.6;
58 // 角度增量
59 this.angleDelta = 0.01 * Math.random();
60 this.speed = 2 + Math.random()
61 }
62 // 原型 对象实例所共享
63 SnowDot.prototype = {
64 createEl: function (a, b) {
65 this.el = document.createElement("img");
66 this.el.setAttribute("src", b + "snow" + Math.floor(Math.random() * 4) + ".gif");
67 this.el.style.position = "absolute";
68 this.el.style.display = "block";
69 this.el.style.zIndex = "99999";
70 this.parent.appendChild(this.el)
71 },
72 move: function () {
73 if (this.angle < this.minAngle || this.angle > this.maxAngle) this.angleDelta = -this.angleDelta;
74 this.angle += this.angleDelta;
75 // 利用正弦波 余弦波(注意波形图在 pi/2 附近的取值)
76 this.left += this.speed * Math.cos(this.angle * Math.PI);
77 this.top -= this.speed * Math.sin(this.angle * Math.PI);
78 if (this.left < 0) this.left = this.maxLeft;
79 else if (this.left > this.maxLeft) this.left = 0
80 },
81 draw: function () {
82 this.el.style.top = Math.round(this.top) + "px";
83 this.el.style.left = Math.round(this.left) + "px"
84 },
85 remove: function () {
86 this.parent.removeChild(this.el);
87 this.parent = this.el = null
88 }
89 }
90
91 var j = false;
92 addToOnLoad(function () {
93 j = true
94 });
95
96 //开启/关闭 标志
97 var f = true;
98
99 // a : 雪花gif图片所在路径
100 // b : 雪花最大数目
101 window.createSnow = function (a, b) {
102 if (j) {
103 var c = [],
104 m = setInterval(function () {
105 // &&前的为false则后边的语句不再执行
106 f && b > c.length && Math.random() < b * 0.0025 && c.push(new SnowDot(a));
107 !f && !c.length && clearInterval(m);
108 for (var e = getScrollDis().top, n = getWinHeight(), d = c.length - 1; d >= 0; d--) {
109 if (c[d]) {
110 // 雪花超出指定高度
111 if (c[d].top > 700 || c[d].top + c[d].size + 1 > e + n) {
112 c[d].remove();
113 c[d] = null;
114 c.splice(d, 1) //移除数组索引d位置开始1个元素
115 //alert(c[d].top)
116 } else {
117 c[d].move();
118 c[d].draw()
119 }
120 }
121 }
122 },
123 40);
124 // 窗口滚动时 雪花移动相应的距离
125 addEvent(window, "scroll",
126 function () {
127 for (var e = c.length - 1; e >= 0; e--) c[e].draw()
128 })
129 } else addToOnLoad(function () {
130 createSnow(a, b)
131 })
132 };
133 window.removeSnow = function () {
134 f = false
135 };
136
137 })();
源代码：snow.zip 页面内容节选自 阿狸-梦之城堡
来源：https://www.cnblogs.com/mushishi/p/3566711.html