SOURCE

var clientHeight = document.documentElement.clientHeight;
$(window).on('resize', function() {
  var nowClientHeight = document.documentElement.clientHeight;
  if (clientHeight > nowClientHeight) {
    //键盘弹出的事件处理
    $(".loginpage-foot").hide();
    $(".loginpage-header").animate({
      'height': '120px'
    },
    200);
  } else {
    //键盘收起的事件处理
    $(".loginpage-foot").show();
    $(".loginpage-header").animate({
      'height': '210px'
    },
    300);
  }
});

<link rel="stylesheet" href="https://cdn.bootcss.com/weui/1.1.2/style/weui.min.css">
<link rel="stylesheet" href="https://cdn.bootcss.com/jquery-weui/1.2.0/css/jquery-weui.min.css">
<div class="loginpage-header">
  <div class="loginpage-title">
    苏州苏嘉杭高速公路有限公司
  </div>
  <div>
    --固定资产
  </div>
</div>
<div class="loginform-wrapper">
  <input type="text" placeholder="请输入用户名" />
  <input type="password" placeholder="请输入密码" />
  <a href="javascript:;" class="weui-btn weui-btn_primary">
    登 陆
  </a>
</div>
<div class="loginpage-foot">
  Copyright © 苏州路森交通科技有限公司
</div>

body {
  margin: 0;
  padding: 0;
  background-color: #f9f9f9;
  color: #a7a5a5;
  font-family: "微软雅黑";
}

.loginpage-header {
  position: relative;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: vertical;
  -webkit-box-direction: normal;
  -ms-flex-direction: column;
  flex-direction: column;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
  height: 210px;
  padding: 0;
  background: #0f88eb;
  background-image: url(http://sandbox.runjs.cn/uploads/rs/234/bxxwrmn8/ml.png);
  background-size: 100%;
  color: #fff;
}

.loginpage-title {
  font-size: 21px!important;
  font-weight: 700;
  margin-bottom: 5px;
}

.loginform-wrapper {
  padding: 20px 16px;
  text-align: center;
  background-color: white;
}

.loginform-wrapper input {
  width: 90%;
  height: 40px;
  text-indent: 15px;
  border: none;
  border-bottom: 1px solid #e7eaf1;
  outline: none;
}

.loginform-wrapper a {
  width: 90%;
  height: 40px;
  line-height: 40px;
  margin-top: 30px;
  font-size: 16px;
  border-radius: 4px;
  border: none;
  outline: none;
}

.loginpage-foot {
  position: absolute;
  bottom: 8px;
  left: 0;
  right: 0;
  text-align: center;
  font-size: 12px;
  color: #a7a5a5;
  background-color: #f9f9f9;
}