javascript - Twitter Bootstrap Modal scrolling the page up on show

Question

Clicking on a link which triggers a Twitter Bootstrap Modal to pop up is causing the browser to scroll up the page. This behavior is only occurring in Chrome.

Here is a demonstration page:

http://www.turizmburosu.com/test2.aspx

The page has 600 rows of links, causing the page body to exceed window height. If any of these links is clicked, it displays the modal dialog. When in Chrome, clicking any of the links below the initial view will cause the background page to scroll up (not always entirely to the top).

I am use the following function to trigger the display of the Modal:

function test(id, imp) {
    $("#modalLabel").html("Header");
    $("#modalBody").html("Body");
    $("#myModal").modal("show");
}

and the links are of the form:

<a href="" onclick="test();return false;">Test Link ###</a>

I am seeing this behavior in Chrome 22.0.1229.94 m.

Any suggestions/ideas as to why this is happening and how to prevent it?

---

Additional Example

This can be recreated on the Twitter Bootstrap documentation page for the Modal plugin.

Once on the page, simply override the existing data-api to use the JavaScript api instead:

$('#modals a[data-toggle="modal"]').on('click',
  function(e) {
    $('#myModal').modal('toggle');
    return false
  });

Now, if the Launch Demo Modal button is clicked, the page will scroll up when the modal is shown.

Again, this is using Chrome.

Answer 1

Fixed (10/29/2012)

This issue has been fixed since Bootstrap v2.2.0. See commit e24b46... for details.

---

(original answer)

This is due to a bug in the implementation of the Twitter Bootstrap Modal (as of 2.1.1). The root of the problem is that the focus is set to the modal prior to it completing its transition. This will only occur under the condition that

1. the browser supports CSS transitions (and you are using bootstrap-transition.js);
2. the modal has the class fade; and
3. when focus is set to an element outside the current view, the browser will scroll to move it into view (e.g., Chrome, Safari).

It should be noted that this affects both the Data API (markup-based) and the Programmatic API (JS-based). However, the reason it is more noticeable when taking the programmatic approach is because, unlike the Data API, it does not automatically restore focus to the triggering element, and, hence, does not scroll the view back down when the modal is hidden.

More info is available on the Twitter Bootstrap repo under Issue #5336: Modal Scrolls Background Content.

A fix has been merged into the 2.1.2-wip branch, which should be up for release any day now.

Here is a demo using the patch bootstrap-modal.js:

JSFiddle