Making a modal window only show once

Question

I use a Bootstrap modal on the index page of my site, but I only want it to show Once per user visit.
I've tried out the answers shown here: Display A Popup Only Once Per User per-user but the problem I run into is that the javascript "popup" conflicts with my modal "onload". And I'm not sure how to resolve it.

This is my onload function:

$(window).load(function(){
    setTimeout(function() {
        $('#onload').modal('show');},2000);
});

and this is my HTML:

 <div class="modal fade bs-example-modal-lg" tabindex="-1" role="dialog" aria-labelledby="myLargeModalLabel" aria-hidden="true"  id="onload">
   <div class="modal-dialog">
    <!-- Modal content-->
   </div>
 </div>

I tried to wrap the whole modal div with the "popup" div but that did weird things to my website (dimmed the whole page but otherwise did nothing)

I think I need to use a cookie or localStorage but I don't know how to configure them or trigger them from the onload javascript.