Bootstrap 4 with remote Modal

Found the problem: They have removed the remote option in bootstrap 4

remote : This option is deprecated since v3.3.0 and will be removed in v4. We recommend instead using client-side templating or a data binding framework, or calling jQuery.load yourself.

I used JQuery to implement this removed feature.

$('body').on('click', '[data-toggle="modal"]', function(){
        $($(this).data("target")+' .modal-body').load($(this).data("remote"));
    });  

According to official documentation, we can do the follow(https://getbootstrap.com/docs/4.1/components/modal):

$('#exampleModal').on('show.bs.modal', function (event) {
    var button = $(event.relatedTarget) // Button that triggered the modal
    var recipient = button.data('whatever') // Extract info from data-* attributes
    // If necessary, you could initiate an AJAX request here (and then do the updating in a callback).
    // Update the modal's content. We'll use jQuery here, but you could use a data binding library or other methods instead.
    var modal = $(this)
    modal.find('.modal-title').text('New message to ' + recipient)
    modal.find('.modal-body input').val(recipient)
})

So, I believe this is the best approach (works for BS 5 too):

<!-- Button trigger modal -->
<a data-bs-toggle="modal" data-bs-target="#modal_frame" href="/otherpage/goes-here">link</a>

<!-- Modal -->
<div class="modal fade" id="modal_frame" tabindex="-1" aria-labelledby="exampleModalLabel" aria-hidden="true">
  <!-- Completes the modal component here -->
</div>

<script>
  $('#modal_frame').on('show.bs.modal', function (e) {
    $(this).find('.modal-body').load(e.relatedTarget.href);
  });
</script>

e.relatedTarget is the anchor() that triggers the modal.

Adapt to your needs

As some of the other answers and Bootstrap docs indicate, Bootstrap 4 requires handling the show.bs.modal event to load content into the modal. This can be used to either load content from an HTML string, or from a remote url. Here's a working example...

$('#theModal').on('show.bs.modal', function (e) {

    var button = $(e.relatedTarget);
    var modal = $(this);

    // load content from HTML string
    //modal.find('.modal-body').html("Nice modal body baby...");

    // or, load content from value of data-remote url
    modal.find('.modal-body').load(button.data("remote"));

});

Bootstrap 4 Remote URL Demo

---

Another option is to open the modal once data is returned from an Ajax call...

  $.ajax({
       url: "http://someapiurl",
       dataType: 'json',
       success: function(res) {

           // get the ajax response data
           var data = res.body;
           // update modal content
           $('.modal-body').text(data.someval);
           // show modal
           $('#myModal').modal('show');

       },
       error:function(request, status, error) {
           console.log("ajax call went wrong:" + request.responseText);
       }
  });

Bootstrap 4 Load Modal from Ajax Demo