How to check if list is sortable?

I just found out, with the data-interface it is working too:

if ($( '#sortable' ).data( 'sortable' )) {
    // sortable instance exists
}

There was a change in jQuery Version after 2012, so now you can write:

if ($( '#sortable' ).data( 'ui-sortable' )) {
    // sortable instance exists
}

or

if ($( '#sortable' ).is(':ui-sortable')) {
    // sortable instance exists
}

If the list is already sortable, then it should have class ui-sortable.

You could use if ($('#list').hasClass('ui-sortable')) to check it.