Select2 open dropdown on focus

I have a form with multiple text inputs and some select2 elements. Using the keyboard to tab between fields works fine - the Select2 element behaves like a form element and receives focus when tabbing. I was wondering if it is possible to open the dropdown when the Select2 element gets focus.

Here's what I've tried so far:

$("#myid").select2().on('select2-focus', function(){
     $(this).select2('open');
});

But using this code makes the dropdown to open again after a selection is made.

Working Code for v4.0+ ^{^{*(including 4.0.7)}}

The following code will open the menu on the initial focus, but won't get stuck in an infinite loop when the selection re-focuses after the menu closes.

// on first focus (bubbles up to document), open the menu
$(document).on('focus', '.select2-selection.select2-selection--single', function (e) {
  $(this).closest(".select2-container").siblings('select:enabled').select2('open');
});

// steal focus during close - only capture once and stop propogation
$('select.select2').on('select2:closing', function (e) {
  $(e.target).data("select2").$selection.one('focus focusin', function (e) {
    e.stopPropagation();
  });
});

Explanation

Prevent Infinite Focus Loop

Note: The focus event is fired twice

1. Once when tabbing into the field
2. Again when tabbing with an open dropdown to restore focus

We can prevent an infinite loop by looking for differences between the types of focus events. Since we only want to open the menu on the initial focus to the control, we have to somehow distinguish between the following raised events:

Doing so it a cross browser friendly way is hard, because browsers send different information along with different events and also Select2 has had many minor changes to their internal firing of events, which interrupt previous flows.

One way that seems to work is to attach an event handler during the closing event for the menu and use it to capture the impending focus event and prevent it from bubbling up the DOM. Then, using a delegated listener, we'll call the actual focus -> open code only when the focus event bubbles all the way up to the document

Prevent Opening Disabled Selects

As noted in this github issue #4025 - Dropdown does not open on tab focus, we should check to make sure we only call 'open' on :enabled select elements like this:

<!-- language: lang-js --> <pre><code>$(this).siblings('select<b>:enabled</b>').select2('open');</b></code></pre>

Select2 DOM traversal

We have to traverse the DOM a little bit, so here's a map of the HTML structure generated by Select2

Source Code on GitHub

Here are some of the relevant code sections in play:

.on('mousedown' ... .trigger('toggle')
.on('toggle' ... .toggleDropdown()
.toggleDropdown ... .open()
.on('focus' ... .trigger('focus'
.on('close' ... $selection.focus()

It used to be the case that opening select2 fired twice, but it was fixed in Issue #3503 and that should prevent some jank

PR #5357 appears to be what broke the previous focus code that was working in 4.05

Working Demo in jsFiddle & Stack Snippets:

<!-- begin snippet: js hide: true console: true babel: false --> <!-- language: lang-js -->

$('.select2').select2({});

// on first focus (bubbles up to document), open the menu
$(document).on('focus', '.select2-selection.select2-selection--single', function (e) {
  $(this).closest(".select2-container").siblings('select:enabled').select2('open');
});

// steal focus during close - only capture once and stop propogation
$('select.select2').on('select2:closing', function (e) {
  $(e.target).data("select2").$selection.one('focus focusin', function (e) {
    e.stopPropagation();
  });
});

<!-- language: lang-html -->

<link href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.7/css/select2.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.7/js/select2.js"></script>

<select class="select2" style="width:200px" >
  <option value="1">Apple</option>
  <option value="2">Banana</option>
  <option value="3">Carrot</option>
  <option value="4">Donut</option>
</select>

<!-- end snippet -->

Tested on Chrome, FF, Edge, IE11