<div class="user_image">
<a class="click_photo" id="click<?php echo $row["photo_id"]; ?>" href="#modal">
// ...
</div>
<a href="#x" class="overlay" id="modal"></a>
<div class="popup" id="popup"></div>
<a ... data-photo-id="photo123789">...</a>let links = document.querySelectorAll("[data-photo-id]");
for(let i = 0; i < links.length; i++) {
let link = links[i];
link.addEventListener("click", function() {
opendModal(link.getAttribute("href") + link.getAttribute("data-photo-id"));
});
}