JavaScript function on tag is getting executed without calling and even I applied onClick event listener

I am trying to call a javaScript function on click tag. But the function is getting executed automatically when I didn’t click on the link and I have also applied the onClick event listener for the function call but still, it is getting executed

here is the tag

<a id="apply" href="?id='.$id . '"  class="btn btn-default" >Apply For Job</a>

here is function

<script type="text/javascript">

document.getElementById('apply').onclick = function() {
    <?php
    echo $uid=$_SESSION["id"];
$sql=mysqli_query($con,"select * from registration where usr_id='$uid'");
                             $row=mysqli_fetch_array($sql);
                               
                                   $user_id=$row['usr_id'];
                                   echo $user_id;
                                    echo $post=$_GET['id'];

   $sql_post_query=mysqli_query($con,"select * from posts where post_id='$post'"); 
  $row_post_query=mysqli_fetch_array($sql_post_query);
  $pos_title=$row['status_title'];
  $sql1=mysqli_query($con,"select * from job_applications where post_id='$post' && user_id='$uid'"); 
  $row1=mysqli_fetch_array($sql1);
  if($row1)
  {        
//do nothing
  }
else
{
$sql_query=mysqli_query($con,"insert into job_applications(post_id,user_id,post_title,date) values('$post','$user_id','$pos_title',NOW())");
     if($sql_query)
     {
        echo "<script>alert('You have successfully applied for this job')</script>";
   phpAlert( "You have successfully applied for this job" );    
     }

}?>
}​;​

Answer

The reason why it runs without you executing or clicking it is because it is a php code. The php code is ran when the page is first loaded and the ‘onclick’ doesnt stop it. Javascript’s onclick event handles client side events, while PHP is server-sided.

In order to only run the php code when the link is clicked, you need to look into ajax calls or html forms, basically a way to communicate with your server