Issue with prependTo() and hide()

Issue with prependTo() and hide()

I have a JS script that will execute an ajax check every X seconds for new content and if any is found, it will prepend it to the top of a timeline. I wanted to get an effect of it sliding down the other content of the timeline, Heres the script thus far: 
  1. $.get( '/some/url', function ( items ) {
        // Error: Uncaught TypeError: Failed to execute 'getComputedStyle' on 'Window': parameter 1 is not of type 'Element'.
     $( items ).hide().prependTo( ".timeline" ).slideDown();

        // This works fine, just doesn't slide
     //$( items ).prependTo( ".timeline" );
    } );
So the error is the line with the prependTo, it throws the error:

Error: Uncaught TypeError: Failed to execute 'getComputedStyle' on 'Window': parameter 1 is not of type 'Element'.

The weird part is it worked fine a while ago, I just made so many changes/commits, 
that I'm not at all sure what caused it to stop working

Any help would be great! Thanks.