原生JS与CSS3实现重力模拟弹跳登录页：opacity、transition与box-shadow详解

div
{
opacity:0.5;
}

<!DOCTYPE html>
<html>
<head>
 <meta charset="utf-8">
 <title>梦幻登录</title>
 <style type="text/css">
 * {
  margin: 0;
  padding: 0;
  list-style: none;
 }
 body {
  overflow: hidden;
 }
 #bg_wrap {
  width: 100%;
  height: 100%;
  position: absolute;
  left: 0;
  top: 0;
  overflow: hidden;
 }
 #bg_wrap div {
  width: 100%;
  height: 100%;
  position: absolute;
  left: 0;
  top: 0;
  opacity: 0;
  /* 设置透明度 */
  transition: opacity 3s;
 }
 /* nth-of-type(1) *筛选选择器选择第一个*/
 #bg_wrap div:nth-of-type(1) {
  opacity: 1;
 }
 #Login {
  width: 272px;
  height: 300px;
  margin: 200px auto;
 }
 #Login .move {
  position: absolute;
  top: -100px;
  z-index: 999;
 }
 #Login h3 {
  width: 270px;
  font-size: 30px;
  font-weight: 700;
  color: #fff;
  font-family: '微软雅黑';
  text-align: center;
  margin-bottom: 30px;
  cursor: move;
  /* top: 100px; */
 }
 /* #username {
  top: 170px;
 }
 #password {
  top: 225px;
 } */
 #Login input.text {
  width: 270px;
  height: 42px;
  color: #fff;
  background: rgba(45, 45, 45, 0.15);
  border-radius: 6px;
  border: 1px solid rgba(255, 255, 255, 0.15);
  box-shadow: 0 2px 3px 0 rgba(0, 0, 0, 1.0) inset;
  text-indent: 10px;
 }
 #Login input.btn {
  /* top: 280px; */
  background: #ef4300;
  width: 272px;
  height: 44px;
  border-radius: 6px;
  color: #fff;
  box-shadow: 0 15px 30px 0 rgba(255, 255, 255, 0.25) inset, 0 2px 7px 0 rgba(0, 0, 0, 0.2);
  /* -webkit-box-shadow: 0 15px 30px 0 rgba(255, 255, 255, 0.25) inset, 0 2px 7px 0 rgba(0, 0, 0, 0.2);
  -moz-box-shadow: 0 15px 30px 0 rgba(255, 255, 255, 0.25) inset, 0 2px 7px 0 rgba(0, 0, 0, 0.2); */
  border: 0;
  text-align: center;
 }
 /* #Login input.focus {
  outline: none;
  box-shadow: 0 2px 3px 0 rgba(0, 0, 0, 0.2) inset;
 } */
 input::-webkit-input-placeholder {
  color: #fff;
 }
 </style>
</head>
<body>
 <div id="bg_wrap">
  <div><img src="images/1.jpg" width="100%" height="100%"></div>
  <div><img src="images/2.jpg" width="100%" height="100%"></div>
  <div><img src="images/3.jpg" width="100%" height="100%"></div>
 </div>
 <div id="Login">
  <h3 id="title" class="move">User Login</h3>
  <form action="#" method="post" target="_blank">
   <input type="text" placeholder="UserName" name="username" id="username" class="text move">
   <input type="password" placeholder="PassWord" name="password" id="password" class="text move">
   <input type="submit" value="Sign in" class="btn move" id="submit">
  </form>
 </div>
 <script type="text/javascript">
 /*背景渐变*/
 /*function(){} 匿名函数
  ()()   IIFE匿名函数立刻执行，函数自执行体*/
 (function() {
  var timer = null; //声明定时器
  var oImg = document.querySelectorAll('#bg_wrap div') //h5最新元素获取写法获取到的是一组元素
  //querySelector获取单个元素的 兼容ie8
  var len = oImg.length; //3
  var index = 0;
  timer = setInterval(function() {
   oImg[index].style.opacity = 0;
   index++;
   // if(index>=3){
   // index=0;
   // }
   index %= len; //index=index%len求模取余 0%3=0; 1%3=1; 2%3=2; 3%3=0;
   oImg[index].style.opacity = 1;
  }, 2000);
 })();
 // 重力模拟弹跳系统
 (function() {
  /*
  改变定位元素的top值
  达到指定位置之后进行弹跳一次
  多个元素一次运动
  动画序列*/
  var oMove = document.querySelectorAll('.move');
  var oLen = oMove.length;
  var timer = null;
  var timeout = null;
  var speed = 3; //移动距离
  move(oLen - 1);
  function move(index) {
   if (index < 0) {
    clearInterval(timer); //清除循环定时器
    clearTimeout(timeout); //清除延时定时器
    return; //终止函数
   }
   var endTop = 150 + (index * 60); //根据下标计算endTop值
   timer = setInterval(function() {
    speed += 3;
    var T = oMove[index].offsetTop + speed; //设置每一次的top值
    if (T > endTop) {
     T = endTop;
     speed *= -1 //取反，让移动距离变为负数
     speed *= 0.4;
     //慢慢停下来
    }
    oMove[index].style.top = T + 'px';
   }, 20);
   timeout = setTimeout(function() {
    clearInterval(timer);
    index--;
    console.log(9);
    move(index);
    console.log(index);
   }, 900) //过900毫秒之后再执行方法里的代码
  }
 })()
 </script>
</body>
</html>