if ($('#check_id').is(":checked"))
{
// it is checked
}
if($('#checkboxID').is(':checked')){ return true; }
if($("#rule").is(":checked")){
$("#form").submit();
}
var checked = '0'; if($('#checkbox').prop('checked')){ checked = '1'; }
$('#isAgeSelected').click(function() {
$("#txtAge").toggle(this.checked);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js">
</script>
<input type="checkbox" id="isAgeSelected"/>
<div id="txtAge" style="display:none">Age is something</div>