Scripting not working in above code need to validate the user and call the function

JavaScript function not working for validation I have created one servlet , servlet is working fine but just function validation is not working.

Created 7 labels using html but javascript function is not working i need to validate the field from user end which i have to display the message for user if user ignore some field .

`<!DOCTYPE html>
<html>
<head>
    <title>Registration</title>
    <style>
        a {
          text-decoration: none;
          }
          .login-page 
          {
          width: 100%;
          height: 100vh;
          display: inline-block;
          display: flex;
          align-items: center;
          }
          .form-right i
           {
          font-size: 100px;
          }
       </style>
        <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/font/bootstrap-icons.css">
        <link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet">  
</head>
<body>
    <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
        <div class="container-fluid">
          <a class="navbar-brand" href="#">PC</a>
          <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarTogglerDemo02" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation">
            <span class="navbar-toggler-icon"></span>
          </button>
          <div class="collapse navbar-collapse" id="navbarTogglerDemo02">
            <ul class="navbar-nav me-auto mb-2 mb-lg-0">
              <li class="nav-item">
                <a class="nav-link active" aria-current="page" href="#">Home</a>
              </li>
              <li class="nav-item">
                <a class="nav-link active" aria-current="page" href="#">About</a>
              </li>
            </ul>
            <form class="d-flex" action="login.html">
              <button class="btn btn-outline-success" type="submit">Login</button>
            </form>
          </div>
        </div>
      </nav>
      <br><br><br><br><br>
      <div class="login-page bg-light">
        <div class="container">
            <div class="row">
                <div class="col-lg-10 offset-lg-1">
                  <h3 class="mb-3">Register</h3>
                    <div class="bg-white shadow rounded">
                        <div class="row">
                            <div class="col-md-7 pe-0">
                                <div class="form-left h-100 py-5 px-5">
                                    <form action="Registration" method="post" onsubmit="return register_form_validation()" class="row g-4" >
                                    
                                     <div class="col-12">
                                                <label>Username<span class="text-danger">*</span></label>
                                                <div class="input-group">
                                                    <div class="input-group-text"><i class="bi bi-person-fill"></i></div>
                                                    <input type="text" class="form-control" placeholder="Enter Username" name="uname">
                                                </div>
                                            </div>

                                            <div class="col-12">
                                                <label>Password<span class="text-danger">*</span></label>
                                                <div class="input-group">
                                                    <div class="input-group-text"><i class="bi bi-lock-fill"></i></div>
                                                    <input type="password" class="form-control" placeholder="Enter Password" name="pwd">
                                                </div>
                                            </div>
                                    
                                        <div class="col-12">
                                            <label>First Name<span class="text-danger">*</span></label>
                                            <div class="input-group">
                                                
                                                <input type="text" class="form-control" placeholder="Enter First name" name="fname">
                                            </div>
                                        </div>
                                        <div class="col-12">
                                            <label>Middle Name<span class="text-danger">*</span></label>
                                            <div class="input-group">
                                                
                                                <input type="text" class="form-control" placeholder="Enter Middle name" name="mname">
                                            </div>
                                        </div>
                                          <div class="col-12">
                                            <label>Last Name<span class="text-danger">*</span></label>
                                            <div class="input-group">
                                                
                                                <input type="text" class="form-control" placeholder="Enter Last name" name="lname">
                                            </div>
                                        </div>
                                           
                                            <div class="col-12">
                                                <label>Email<span class="text-danger">*</span></label>
                                                <div class="input-group">
                                                    
                                                    <input type="text" class="form-control" placeholder="Enter Email Address" name="email">
                                                </div>
                                            </div>
                                            <div class="col-12">
                                                <label>Mobile Number<span class="text-danger">*</span></label>
                                                <div class="input-group">
                                                    
                                                    <input type="number" class="form-control" placeholder="Enter Mobile Number" name="mobile">
                                                </div>
                                            </div>

                                           
                                            <div class="col-sm-6">
                                                <div>
                                                  
                                                  <button type="submit" class="btn btn-primary px-4 float-end mt-4">Register</button>
                                                </div>
                                            </div>
                                            
                                           
                                            
                                           
                                    </form>
                                </div>
                            </div>
                            <div class="col-md-5 ps-0 d-none d-md-block">
                                <div class="form-right h-100 bg-primary text-white text-center pt-5">
                                  <i class="bi bi-book-half"></i>
                                    <h2 class="fs-1">Welcome to PC bookshop!!!</h2>
                                </div>
                            </div>
                        </div>
                    </div>
                    <p class="text-end text-secondary mt-3"></p>
                </div>
            </div>
        </div>
    </div>
    <script>
        function register_form_validation()
        {
          var uname=document.getElementById("uname").value;
          var pwd=document.getElementById("pwd").value;
          var email=document.getElementById("email").value;
          var fname=document.getElementById("fname").value;
          var mname=document.getElementById("mname").value;
          var lname=document.getElementById("lname").value;
          var mobile=document.getElementById("mobile").value;
        
       
          if(uname=='')
          {
            alert('Please enter Username');
          return false;
         }
        else if(pwd=='')
           {
          alert('Please enter Email');
          return false;
           }
        else if(email=='')
           {
          alert('Please enter password');
          return false;
           }
        else if(fname=='')
           {
          alert('Please enter fname');
          return false;
           }
        else if(mname=='')
           {
          alert('Please enter mname');
          return false;
           }
        else if(lname=='')
           {
          alert('Please enter lname');
          return false;
           }
        else if(mobile=='')
           {
          alert('Please enter mobile');
          return false;
           }
        else
        {
          return true;
        }
         
        return false;
        }
       
    </script> 
</body>
</html>`