Determining if one-liner span has ellipsis overflow

ellipsis-detection.js

function getVisibleWidth(elem) {
	// cross browser, returns decimals for ultra-precision
	return elem.getBoundingClientRect().right - elem.getBoundingClientRect().left; 
}

function getNaturalWidth(elem) {
	var old = {
		overflow: elem.style.overflow,
		width: elem.style.width,
		display: elem.style.display
	}, result;

    elem.style.overflow = 'visible';
    elem.style.width = 'auto';
    elem.style.display = 'inline-block';
    result = getVisibleWidth(elem);
    elem.style.overflow = old.overflow;
    elem.style.width = old.width;
    elem.style.display = old.display;

    return result;
}

function hasEllipsis(elem) {
    function getStyle(style) {
    	if (window.getComputedStyle) {
    		return window.getComputedStyle(elem)[style]; // modern browsers
    	} else {
    		return elem.currentStyle[style]; // IE
    	}
    }

    var ellipsisConfigured = getStyle('overflow') === 'hidden' || getStyle('text-overflow') === 'ellipsis';

    if (ellipsisConfigured) {
        visibleWidth = getVisibleWidth(elem);
		naturalWidth = getNaturalWidth(elem);

	    return visibleWidth < naturalWidth;
    } else {
    	return false;
    }
}

Tested in IE8 standards mode. Screw quirks mode.