forms - Tri-state Check box in HTML?

Question

There is no way to have a tri-state check button (yes, no, null) in HTML, right?

Are there any simple tricks or work-arounds without having to render the whole thing by oneself?

Answer 1

Edit — Thanks to Janus Troelsen's comment, I found a better solution:

HTML5 defines a property for checkboxes called indeterminate

See w3c reference guide. To make checkbox appear visually indeterminate set it to true:

element.indeterminate = true;

Here is Janus Troelsen's fiddle. Note, however, that:

• The indeterminate state cannot be set in the HTML markup, it can only be done via Javascript (see this JSfiddle test and this detailed article in CSS tricks)

• This state doesn't change the value of the checkbox, it is only a visual cue that masks the input's real state.

• Browser test: Worked for me in Chrome 22, Firefox 15, Opera 12 and back to IE7. Regarding mobile browsers, Android 2.0 browser and Safari mobile on iOS 3.1 don't have support for it.

Previous answer

Another alternative would be to play with the checkbox transparency for the "some selected" state (as Gmail does used to do in previous versions). It will require some javascript and a CSS class. Here I put a particular example that handles a list with checkable items and a checkbox that allows to select all/none of them. This checkbox shows a "some selected" state when some of the list items are selected.

Given a checkbox with an ID #select_all and several checkboxes with a class .select_one,

The CSS class that fades the "select all" checkbox would be the following:

.some_selected {
    opacity: 0.5;
    filter: alpha(opacity=50);
}

And the JS code that handles the tri-state of the select all checkbox is the following:

$('#select_all').change (function ()
{
    //Check/uncheck all the list's checkboxes
    $('.select_one').attr('checked', $(this).is(':checked'));
    //Remove the faded state
    $(this).removeClass('some_selected');
});

$('.select_one').change (function ()
{
  if ($('.select_one:checked').length == 0)
      $('#select_all').removeClass('some_selected').attr('checked', false);
  else if ($('.select_one:not(:checked)').length == 0)
      $('#select_all').removeClass('some_selected').attr('checked', true);
  else
      $('#select_all').addClass('some_selected').attr('checked', true);
});

You can try it here: http://jsfiddle.net/98BMK/

Hope that helps!