How do I check if a checkbox is checked with JQuery?

I am trying to allow a click function if the user has checked a checkbox on the page. Otherwise, I want to add a class to the #additional_foreign开发者_如何学编程 button.

I think I am close, but it doesn't seem to be working. Here is my code:

if($('#foreign_checkbox').attr('checked')) { 
    $('#additional_foreign').click(function() {
        alert('This click function works');
    });
} else {
    $('#additional_foreign').addClass('btn_disable');   
}

When I check the checkbox, it doesn't allow the click function and when I uncheck the checkbox, it also doesn't add the class as it should.

What am I doing wrong?

EDIT:Here is my HTML for clarification.

<input id="foreign_checkbox" type="checkbox" />
<span id="additional_foreign">Click Me</span>

try using $('#foreign_checkbox').is(":checked") - rest of the code looks fine

If this was my code I'd do something like this to make it work:

<input id="foreign_checkbox" type="checkbox" />
<span style='display:none' id="additional_foreign">Click Me</span>

<script type="text/javascript">
    $(document).ready(function() {

        $("#foreign_checkbox").click(function() {
            if($('#foreign_checkbox').is(':checked')) { 
                $('#additional_foreign').show();
            } else {
                $('#additional_foreign').hide();
            }
        });

        $('#additional_foreign').click(function() {
            alert('This click function works');
        });
    });
</script>

The problem is that the code doesn't run continually, only when the page loads, when all the boxes are unchecked. You need an action that fires when the box is checked or unchecked, which adds an action or a class to the button:

$('#foreign_checkbox').change(function(){
    if (this.checked){
        $('#additional_foreign').click(function() {
           doSomething();
        });
    } else {
        $('#additional_foreign').addClass('btn_disable');
    }   
});