element is hidden jquery

// Checks CSS content for display:[none|block], ignores visibility:[true|false]
$(element).is(":visible");

// The same works with hidden
$(element).is(":hidden");

// Checks css for display:[none|block], ignores visibility:[true|false]
$(element).is(":hidden"); 

$('#yourid').attr('hidden', false);
$('#yourid').attr('hidden', true);

$(':checkbox').change(function(){
    $('#delete').removeAttr('hidden');
});