getWidth = function(elem, parent, width){
		width = width || elem.offsetWidth;

		while(width < lazySizesCfg.minSize && parent && !elem._lazysizesWidth){
			width =  parent.offsetWidth;
			parent = parent.parentNode;
		}

		return width;
	}
@param elem { Element }
@param parent { Element }
@param [width] {number}
@returns {number}