jQuery: Error if class not found

This causes a JavaScript error on pages that do NOT contain:

<a href="hello/" class="hello selected"><em>Hello</em></a>

If no link has a class of selected I get a JavaScript error.
$('#menuSide a.selected').find("em").css({'background-position': $('#menuSide a.selected').find("em").css("background-position").match(/([^\s]+)/)[0] + ' -13px'});

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Gurvinder Pal SinghCommented:
it is because background-position property is null.

did you tried after setting background-position property?

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Gurvinder Pal SinghCommented:
try this code

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
	<script src="jquery-1.4.2.min.js"></script>
			var backgroundPosition = $('#menuSide a.selected').find("em").css("background-position");

			if ( !backgroundPosition || backgroundPosition.length == 0)
				alert("background-position is not set");

			var abc = backgroundPosition.match(/([^\s]+)/)[0] + ' -13px';
			$('#menuSide a.selected').each(function(){
				$(this).find("em").css('background-position', abc);

	<div id="menuSide">
		<a href="hello/" class="hello selected">

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hankknightAuthor Commented:
How can I get it to work even if the CSS has not set a background position for an item on that page?  I think this should be fixed with JavaScript not CSS.
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Gurvinder Pal SinghCommented:
you can assume background position to be center (50%), if not given.
May be depending upon browser, it may vary
hankknightAuthor Commented:
OK, I see what you mean,  thanks.  This works:
if ($('#menuSide a.selected').find("em").css("background-position")) $('#menuSide a.selected').find("em").css({'background-position': $('#menuSide a.selected').find("em").css("background-position").match(/([^\s]+)/)[0] + ' -13px'});

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Gurvinder Pal SinghCommented:
yes, or you can refactor that part out.

well, you are a master yourself :)
hankknightAuthor Commented:
Thanks for the help.  I am still trying to master jQuery!

This also revealed a problem with IE, but I will ask a related question about that.
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