Are there side effects to using string concatenation or jQuery inside jquery selectors?

...
    <script type="text/javascript">
        var a = 'y';
        $(document).ready(function() {
            $('p[id^=' + $('p[id=x]').html() + a + "]").css('color','blue');
        });
    </script>
...

<p id="x">2a</p>
<p id="2ay_">mytext</p>