javascript代码为啥加载不出来呀

html代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8"/>
    <meta http-equiv="X-UA-Compatible" content="IE=edge"/>
    <meta name="viewport" content="width=device-width, initial-scale=1"/>
    <title>用户注册</title>
    <link rel="stylesheet" href="css/footer.css">
    <link href="css/bootstrap.min.css" rel="stylesheet">
    <script src="js/jquery-2.2.4.min.js"></script>
    <script src="js/bootstrap.min.js"></script>
    <script type="text/javascript"></script>
    <script type="text/javascript" src="js/include.js"></script>
    <style>
        .myclass{
            width: 100%;
            height: 70%;
            background-image: url(images/register_bac.jpg);
            background-size: 100% 100%;position: relative;
        }
    </style>
    <script type="text/javascript" src="js/register.js"></script>
</head>
<body>
<div id="header"></div>
<div class="myclass">
    <div align="center" style="padding: 100px;">
        <form action="javascript:location.href='registerUserServlet'" id="register" method="post">
            <div>
                <label for="username"><h3>用户名：</h3></label>
                <input type="text" name="username" placeholder="请输入8-20位的用户名" id="username"style="height: 45px;width: 200px">
                <br> <span id="namespan" style="color: #f40;height: 10px;width: 10px"></span>
            </div>
            <div>
                <label for="password"><h3>密 &nbsp; 码：</h3></label>
                <input type="password" name="password" placeholder="请输入8-20位密码" id="password" style="height: 45px;width: 200px">
                <br> <span id="passpan" style="color: #f40;height: 10px;width: 10px"></span>
            </div>
            <div>
                <label for="repassword"><h3>确认密码：</h3></label>
                <input type="password" name="repassword" placeholder="请输入8-20位密码" id="repassword" style="height: 45px;width: 200px">
                <br> <span id="repasspan" style="color: #f40;height: 10px;width: 10px"></span>
            </div>
            <div>
            <span>
                <label for="checkCode"><h3>验证码：</h3></label>
            <input type="text" name="checkCode" id="inputCode" placeholder="验证码" style="height: 45px;width: 120px" >
            <img src="checkCodeServlet" id="checkCode"
                 title="看不清换一张" name="checkCode" id="flashCode" style="width: 75px;height: 45px"></span><br/>
                <br> <span id="CheckCodeSpan" style="color: #f40;height: 10px;width: 10px"></span>
            </span>
            </div>
            <div>
                <input type="submit" value="注册" name="login" style="width: 150px;height: 45px" onclick="">
            </div>
        </form>
        <div align="center">
            <a href="logs.html">已有用户登录 </a>|
            <a href="error/setpassworder.html">忘记密码 &nbsp; 找回密码</a>
        </div>

    </div>

</div>
<div id="footer"></div>
</body>
</html>

function checkcode() {
    document.getElementById("checkCode").src=
        "checkCodeServlet?time="+new Date().getTime();
}
function checkUsername() {
    //校验用户名
    var username = $("#username").val();
    var namespan = $("#namespan");
    //定义正则表达式，8到20位
    var re_username=/^w{8,20}$/;
    var flag = re_username.test(username);
    if (flag){
        $("#namespan").hide();
        $.ajax({
            url:"RegisterFindUserServlet",
            type: "post",
            data: {"username":username,"userExist":"","msg":""},
            success:function (data) {
                data=JSON.parse(data);
                if(! data.userExist)
                {
                    namespan.style.color = "green";
                }else{
                    namespan.style.color = "red";
                }
                namespan.innerHTML=data.msg;
                $("#namespan").show();
                return false;
            },
            error:function (data) {
                alert("出错了")
            }
        });
    }else{
        namespan.innerHTML="用户名不合法";
        $("#namespan").show();
        return flag;
    }

}
function checkPass() {
    //校验密码
    var password = $("#password").val();
    var passpan = $("#passpan");
    var re_password=/^w{8,20}$/;
    var flag = re_password.test(password);
    if (flag){
        passpan.style.color = "green";
        passpan.innerHTML="密码可用";
        passpan.show();
    }else{
        //passpan.style.color = "green";
        passpan.innerHTML="密码不合法";
        // passpan.style.color="red";
        passpan.show();
    }
    return flag;
}
function checkRePass() {
    //校验确认密码
    if($("#password").val() != null || $("#password").val() != ""){
        if($("#repassword").val() != null ||$("#repassword").val() != "" ){
            if($("#repassword").val() !=  $("#password").val()){
                $("#repasspan").innerHTML="与之前密码不同";
                $("#repasspan").show();
                return false;
            }else{
                $("#repasspan").hide();
            }
        }else{
            $("#repasspan").hide();
        }
    }else{
        $("#repasspan").hide();
    }
    return true;
}
function checkCode() {
    //校验验证码
    var code = $("#inputCode").val();
    if(code == null || code == ""){
        $("#codespan").innerHTML="验证码不能为空";
        $("#codespan").show();
        return false;
    }else {
        $("#codespan").hide();
        return true;
    }
}
$(function () {
    $("#register").submit(function () {
        //只有所有校验均为true才提交表单
        return checkCode()&&checkPass()&&checkRePass()&&checkUsername();
    });
    $("#username").blur(checkUsername);
    $("#password").blur(checkPass);
    $("#repassword").blur(checkRePass);
    $("#checkCode").blur(checkCode);
    $("#flashCode").click(checkcode);
})

控制台报错了吗？

你把放到

你把js的导入的顺序调换一下

你的方法这样写 var checkUsername = function() {}

解决了没