Funciones para obtener el ancho y alto del viewport en javascript

gistfile1.js

function getViewPortHeight() {
	var viewportheight;
	if (typeof window.innerWidth != 'undefined') {
	    viewportheight = window.innerHeight;
		// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
	} else if (typeof document.documentElement != 'undefined'   && typeof document.documentElement.clientWidth != 'undefined' && document.documentElement.clientWidth != 0) {
       viewportheight = document.documentElement.clientHeight;
	} else {
		viewportheight = document.getElementsByTagName('body')[0].clientHeight;
	}
	return viewportheight;
		
}
function getViewPortWidth() {
	var viewportwidth;
	// the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight
	if (typeof window.innerWidth != 'undefined') {
		viewportwidth = window.innerWidth;
		// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
	} else if (typeof document.documentElement != 'undefined'   && typeof document.documentElement.clientWidth != 'undefined' && document.documentElement.clientWidth != 0) {
		viewportwidth = document.documentElement.clientWidth;
		// older versions of IE
	} else {
       viewportwidth = document.getElementsByTagName('body')[0].clientWidth;
	}
	return viewportwidth;
}