Someone

function setMenuBorder() {
	var leftpane = document.getElementById('leftpane');
	var mainpane = document.getElementById('mainpane');
	
	if (leftpane.offsetHeight > mainpane.offsetHeight) {
		alert('LEFT!');
		leftpane.style.borderRight = "1px solid #E7E7E7";
	} else {
		alert('RIGHT!');
		mainpane.style.borderLeft = "1px solid #E7E7E7";
	}
}