Javascript 从输入jquery获取值

我试图从输入中获取值，并通过脚本将其传递给注册用户，但没有运气存储它。我设置为测试的警报不显示任何值。下面是我必须为用户名获取值并在脚本中传递的内容：

                    <form id ="form-signin" class="form-signin" action="" method="">
                      <input type="text" id="username" class="form-control" placeholder="Username" required autofocus>
                      <input type="email" class="form-control" placeholder="Email" required autofocus>
                      <input type="password" class="form-control" placeholder="Password" required>
                      <input type="submit" id="createUser" class="btn btn-lg btn-default btn-block" value="Sign Up" />
                    </form>



<script type="text/javascript">

    Parse.initialize("u3BTp3Efoko8hbNhl5MCeli8Kd2iiEk8mE4vYgn4", "tQEGymAWeB8Tr2LA3YDGoq2Lt2xpGMW9ikeFSTtD");

    //get the input data
    var username = $('#username').val();

    //set the user
    var user = new Parse.User();

    $( "form" ).submit(function( event ) {

      alert( "Error: " + username + " " );

        user.set("username", " " + username + " ");
        user.set("password", "my pass");
        user.set("email", "email@example.com");

        // other fields can be set just like with Parse.Object
        user.set("phone", "415-392-0202");

        user.signUp(null, {
          success: function(user) {
            // Hooray! Let them use the app now.
          },
          error: function(user, error) {
            // Show the error message somewhere and let the user try again.
            alert("Error: " + error.code + " " + error.message);
          }
        });

    });

</script>

解析初始化（“u3btp3efoko8hbnhl5mceli8kd2iek8me4vygn4”，“tQEGymAWeB8Tr2LA3YDGoq2Lt2xpGMW9ikeFSTtD”）；
//获取输入数据
var username=$（'#username'）.val（）；
//设置用户
var user=new Parse.user（）；
$（“表格”）。提交（功能（事件）{
警报（“错误：+username+”）；
user.set（“用户名”，“用户名+”）；
设置（“密码”、“我的通行证”）；
user.set（“电子邮件”email@example.com");
//其他字段可以像Parse.Object一样设置
用户设置（“电话”，“415-392-0202”）；
user.signUp（null{
成功：功能（用户）{
//万岁！让他们现在就使用这个应用。
},
错误：函数（用户，错误）{
//在某个地方显示错误消息，然后让用户重试。
警报（“错误：+Error.code+”“+Error.message”）；
}
});
});

您需要在提交处理程序中读取用户名的值

加载空白页面时，您正在读取字段

#username

的值，一旦读取值并将其分配给变量，变量值将不会在更新输入值时更新

//dom ready handler
jQuery(function ($) {
    Parse.initialize("u3BTp3Efoko8hbNhl5MCeli8Kd2iiEk8mE4vYgn4", "tQEGymAWeB8Tr2LA3YDGoq2Lt2xpGMW9ikeFSTtD");

    //set the user
    var user = new Parse.User();

    $("form").submit(function (event) {
        //get the input data
        var username = $('#username').val();//read the user value in s

        alert("Error: " + username + " ");

        user.set("username", " " + username + " ");
        user.set("password", "my pass");
        user.set("email", "email@example.com");

        // other fields can be set just like with Parse.Object
        user.set("phone", "415-392-0202");

        user.signUp(null, {
            success: function (user) {
                // Hooray! Let them use the app now.
            },
            error: function (user, error) {
                // Show the error message somewhere and let the user try again.
                alert("Error: " + error.code + " " + error.message);
            }
        });

    });
})