JavaScript and Jquery If Statment Append

Ok so I have a list and some of the text inside the list is to long so I want to use JavaScript and Jquery to trim the text and add ... to the end of the test if its longer than 30 characters.

<ul>
    <li><a href="#">Long List item Long List item Long List item </a></li>
    <li><a href="#">Smaller List item</a></li>
    <li><a href="#">item</a></li>
</ul>

My Jquery at the moment:

$(function(){
    $("ul li a").html(function(){
        return $(this).html().substring(0,30);
    });
    $('.box ul li a').append(' ...');
});

This works but I want to add maybe an IF statment to only add the ... if the length of the text inside of the tag is more than 30 characters. How would I go about doing that?

Thanks