Get Viewport dimensions

getViewportDimensions

function _getViewportDimensions() {
	var dEl = document.documentElement,
		clientH = dEl['clientHeight'],
		innerH = window['innerHeight'],
		clientW = dEl['clientWidth'],
		innerW = window['innerWidth'];
	
	return {
		height : ( clientH < innerH ) ? innerH : clientH,
		width : ( clientW < innerW ) ? innerW : clientW
	};
}