如何解决不断收到错误：未捕获的类型错误：无法读取未定义的属性“querySelector”？

我收到一个错误，上面写着未捕获的类型错误：在日期验证时无法读取未定义的属性“querySelector”。 任何帮助将不胜感激。

这是我的 JSP 页面表单

  <form id="reg-form" action="RegisterServlet" methods="POST">
                                      
                                            <div>
                                              <label for="user_name">UserName</label>
                                              
                                              <input name="user_name" type="text"id="username" placeholder="Enter name">
                                              <small></small>

                                            </div>
                                            <div>
                                              <label for="user_email">Email address</label>
                                              <input name="user_email" type="email"id="email" aria-describedby="emailHelp" placeholder="Enter Email">
                                             
                                                 <small></small>

                                            </div>
                                            <div>
                                              <label for="user_password">Password</label>
                                              <input name="user_password" type="password"id="password" placeholder="Enter password">
                                                   <small></small>

                                            </div>
                                      
                                            <div> 
                                              <label for="confirm_password">Confirm Password</label>
                                              <input type="password" placeholder="confirm Password" name="confirm_password"id="confirm-password" >
                                                <small></small>
                                             </div>
                                      
                                            <div> 
                                            <label for="user_dob">Date of Birth</label>
                                            <input type="text" placeholder="Enter dob"name="user_dob" id="dob" >
                                              <small></small>
                                            </div>
                                      
                                           
                                            <div>
                                              <label for="user_regid">Registration ID</label>
                                              <input type="text" name="user_regid"id="regid" aria-describedby="regid" placeholder="Enter Reg. ID">
                                                 <small></small>

                                            </div>
                                      
                                             <div>
                                              <label for="user_rollno">Roll No.</label>
                                              <input type="text" name="user_rollno"id="roll" aria-describedby="year" placeholder="(e.g) 31384">
                                                 <small></small>

                                            </div>
                                      
                                           
                                      
                                            <div>
                                              <label for="user_no">Contact No.</label>
                                              <input type="text"name="user_no"  id="" aria-describedby="year" placeholder="Enter 10-digit phone number">
                                                  <small></small>

                                            </div>
                                      
                                           
                                      
                                          
                                      
                                      
                                            <div>
                                              <input type="checkBox" name="user_check"id="exampleCheck1">
                                              <labelfor="exampleCheck1">I Agree terms and conditions</label>
                                            </div>
                                      
                                      
                                      <br>
                                      <divhttps://www.jb51.cc/tag/dis/" target="_blank">display: none" id="loader">
                                      <span></span>
                                      <h4> Please wait...</h4>
                                      </div>
                                      <br>
                                            <button id="submit"  type="submit">Submit</button>
                                          </form>

这是发生错误的部分（日期验证）

 <div> 
 <label for="user_dob">Date of Birth</label>
  <input type="text" placeholder="Enter dob"name="user_dob" id="dob" >
  <small></small>
  </div>

这是我的 JS 代码，只发布了发生错误的部分。

const dateE1=document.getElementById(''dob'');

const debounce = (fn,delay = 500) => {
    let timeoutId;
    return (...args) => {
        // cancel the prevIoUs timer
        if (timeoutId) {
            clearTimeout(timeoutId);
        }
        // setup a new timer
        timeoutId = setTimeout(() => {
            fn.apply(null,args)
        },delay);
    };
};


form.addEventListener(''input'',debounce(function (e) {
    switch (e.target.id) {
        case ''username'':
            checkUsername();
            break;
        case ''email'':
            checkEmail();
            break;
        case ''password'':
            checkPassword();
            break;
        case ''confirm-password'':
            checkConfirmPassword();
            break;
        case ''dob'':
            checkDate();
            break;
    }
}));

const checkDate = () => {

    let valid = false;

   

    const mydate = dateE1.value.trim();

    if (!isrequired(mydate)) {
        showError(mydate,''date cannot be blank'');
    } 
    else {
        showSuccess(mydate);
        valid = true;
    }
    return valid;
};

const isrequired = value => value === '''' ? false : true;

const showError = (input,message) => {
    // get the form-field element
    const formField = input.parentElement;
    // add the error class


    // show the error message    const error = formField.querySelector(''small'');

    const error = formField.querySelector(''small'');
    error.textContent = message;
};

const showSuccess = (input) => {
    // get the form-field element
    const formField = input.parentElement;



    // hide the error message
    const error = formField.querySelector(''small'');
    error.textContent = '''';
}

任何帮助将不胜感激

解决方法

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    const sideBySideMap = L.control.splitMap(
        L.tileLayer(tiles[leftTileIndex]._url,{
            tms: true,opacity: 1,attribution: "",minZoom: 1,maxZoom: 16,}),L.tileLayer(tiles[rightTileIndex]._url,''padding: 50;'',})
    );

    useEffect(() => {
        if (map) {
            sideBySideMap.addTo(map);
        }
    },[map]);