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+<!DOCTYPE html>
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+<html lang="en">
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+<head>
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+ <meta charset="UTF-8">
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+ <meta http-equiv="X-UA-Compatible" content="IE=edge">
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+ <meta name="viewport" content="width=device-width, initial-scale=1.0">
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+ <title>Document</title>
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+ <style>
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+ img{
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+ position: absolute;
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+ }
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+ </style>
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+</head>
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+<body>
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+ <script>
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+ //获取屏幕的宽度
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+ var screenWidth = document.body.clientWidth || document.documentElement.clientWidth
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+ //获取屏幕的高度
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+ var screenHeight = document.body.clientHeight || document.documentElement.clientHeight
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+ //构造函数 写属性
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+ function leaf(){
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+ this.width = Math.random() * 100 + 100
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+ //screenWidth - this.width 最大的距离
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+ this.xLeft = Math.random() * (screenWidth - this.width)
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+ this.xTop = 0
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+ //Math.random() 0->1 之间的随机小数
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+ //'img/1.png'
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+ // 1 - 4 随机整数
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+ //Math.random() * 4 0->4 之间的随机小数 不包括4
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+ //Math.random() * 4 + 1 1->5之间的随机小数 不包括5
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+ //Math.floor() 向下取整
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+
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+ //Math.floor(Math.random() * 4 + 1) 1->5之间的随机小数向下取整 1 2 3 4
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+
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+ this.bg = 'img/'+ Math.floor(Math.random() * 4 + 1) +'.png'
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+ }
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+
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+ //原型下面 写方法
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+ //<img src="">
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+ leaf.prototype.init = function(){
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+ var oImg = document.createElement('img')
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+ oImg.src = this.bg
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+ oImg.style.width = this.width + 'px'
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+ oImg.style.left = this.xLeft + 'px'
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+ oImg.style.top = this.xTop + 'px'
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+ document.body.appendChild(oImg)
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+ }
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+ for(var i=0;i<20;i++){
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+ var leaf1 = new leaf()
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+ leaf1.init()
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+ }
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+ </script>
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+</body>
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+</html>
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zsydgithub
