检测用户名和密码

  <input type="text" id="txtUserName">
  <input type="text" id="txtUserPassword">
  <input type="button" id="btnLogin" value="登陆">

  <script>
    //1.获取登陆按钮
    var btnLogin = document.getElementById('btnLogin');
    btnLogin.onclick = function () {

      //2.判断用户名3-6位
      var txtUserName = document.getElementById('txtUserName');
      if (txtUserName.value.length < 3 || txtUserName.value.length > 6) {
        txtUserName.style.background = "yellow";
        return;
      } else {
        txtUserName.style.background = "none";
      }

      //3.判断密码6-8位
      var txtUserPassword = document.getElementById('txtUserPassword');
      if (txtUserPassword.value.length < 6 || txtUserPassword.value.length > 8) {
        txtUserPassword.style.background = "yellow";
        return;
      } else {
        txtUserPassword.style.background = "none";
      }

      console.log("登陆成功");
    }

  </script>