Passing data to a bootstrap modal

I think you can make this work using jQuery's .on event handler.

Here's a fiddle you can test; just make sure to expand the HTML frame in the fiddle as much as possible so you can view the modal.

http://jsfiddle.net/8c05pn1f/

HTML

<p>Link 1</p>
<a data-toggle="modal" data-id="ISBN564541" title="Add this item" class="open-AddBookDialog btn btn-primary" href="#addBookDialog">test</a>

<p>&nbsp;</p>


<p>Link 2</p>
<a data-toggle="modal" data-id="ISBN-001122" title="Add this item" class="open-AddBookDialog btn btn-primary" href="#addBookDialog">test</a>
    
<div class="modal hide" id="addBookDialog">
 <div class="modal-header">
    <button class="close" data-dismiss="modal">×</button>
    <h3>Modal header</h3>
  </div>
    <div class="modal-body">
        <p>some content</p>
        <input type="text" name="bookId" id="bookId" value=""/>
    </div>
</div>

JAVASCRIPT

$(document).on("click", ".open-AddBookDialog", function () {
     var myBookId = $(this).data('id');
     $(".modal-body #bookId").val( myBookId );
     // As pointed out in comments, 
     // it is unnecessary to have to manually call the modal.
     // $('#addBookDialog').modal('show');
});

Here's how I implemented it working from @mg1075's code. I wanted a bit more generic code so as not to have to assign classes to the modal trigger links/buttons:

Tested in Twitter Bootstrap 3.0.3.

HTML

<a href="#" data-target="#my_modal" data-toggle="modal" data-id="my_id_value">Open Modal</a>

JAVASCRIPT

$(document).ready(function() {

  $('a[data-toggle=modal], button[data-toggle=modal]').click(function () {

    var data_id = '';

    if (typeof $(this).data('id') !== 'undefined') {

      data_id = $(this).data('id');
    }

    $('#my_element_id').val(data_id);
  })
});

Here is a cleaner way to do it if you are using Bootstrap 3.2.0.

Link HTML

<a href="#my_modal" data-toggle="modal" data-book-id="my_id_value">Open Modal</a>

Modal JavaScript

//triggered when modal is about to be shown
$('#my_modal').on('show.bs.modal', function(e) {

    //get data-id attribute of the clicked element
    var bookId = $(e.relatedTarget).data('book-id');

    //populate the textbox
    $(e.currentTarget).find('input[name="bookId"]').val(bookId);
});

http://jsfiddle.net/k7FC2/

Bootstrap 4.3 - use code from below snippet - more here

$('#exampleModal').on('show.bs.modal', function (event) {
  let bookId = $(event.relatedTarget).data('bookid') 
  $(this).find('.modal-body input').val(bookId)
})

a.btn.btn-primary.open-AddBookDialog {color: white }

<!-- Initialize Bootstrap 4 -->

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>

<!-- BUTTON -->

<a 
  class="btn btn-primary open-AddBookDialog" 
  data-toggle="modal" 
  data-target="#exampleModal" 
  data-bookid="@book.Id" 
  title="Add this item"
>Open</a>

<!-- MODAL -->

<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
    
      <div class="modal-body">
        <input type="hidden" name="bookId" id="bookId" value=""/>
        <input type="text" class="form-control" id="recipient-name">    
      </div>
      
      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
      </div>

    </div>
  </div>
</div>