Javascript: Background Position control by js, IE8 included

gistfile1.txt

var backgroundPos,
	xPos,
	yPos;
	
if( $j("html").hasClass("ie8")) { // html class... you know... it's useful
	xPos = $j(this).css("background-position-x");
	yPos = Number($j(this).css("background-position-y").replace(/[^0-9-]/g, ''));
} else {
	backgroundPos = $j(this).css("backgroundPosition").split(" ");
	xPos = backgroundPos[0],
	yPos = Number(backgroundPos[1].replace(/[^0-9-]/g, ''));
}

yPos = yPos + 310; // this value will be the y shift distance in your background image

$j(this).css("backgroundPosition", xPos + " " + yPos+ "px");