Media Queries for everybody

mediaquery.js

(function () {
	var
	documentElement = document.documentElement,
	viewportFontSize, viewportHeight, viewportIsPortrait, viewportMax, viewportMin, viewportWidth;

	function getViewportFontSize() {
		var
		body = documentElement.appendChild(document.createElement('body')),
		iframe = document.createElement('iframe'),
		iframeDocument;

		iframe.style.cssText = 'clip:rect(0 0 0 0);position:absolute';

		body.appendChild(iframe);

		iframeDocument = iframe.contentWindow.document;

		iframeDocument.write('<div style=height:1em;overflow:hidden>');
		iframeDocument.close();

		viewportFontSize = iframeDocument.body.lastChild.clientHeight;

		documentElement.removeChild(body);
	}

	function getViewportSize() {
		viewportHeight = Math.max(documentElement.clientHeight, documentElement.offsetHeight);
		viewportWidth = Math.max(documentElement.clientWidth, documentElement.offsetWidth);
		viewportMax = Math.max(viewportHeight, viewportWidth);
		viewportMin = Math.min(viewportHeight, viewportWidth);
		viewportIsPortrait = viewportHeight > viewportWidth;
	}

	function replace() {
		var args = arguments, index = 0, string = args[0];

		while (++index in args) {
			string = string.replace(args[index], args[++index]);
		}

		return string;
	}

	function computeCSSValue(length, unit) {
		return length * replace(unit,
			/cm/, 37.7952,
			/r?em/, viewportFontSize,
			/in/, 96,
			/mm/, 3.77952,
			/pc/, 16,
			/pt/, 4 / 3,
			/px/, 1,
			/vh/, viewportHeight,
			/vmax/, viewportMax,
			/vmin/, viewportMin,
			/vw/, viewportWidth
		);
	}

	function evaluateMediaQuery(query) {
		return new Function('e', 'try{return ' + replace(String(query || 1).toLowerCase(),
			// ignore `only`
			/^only\s+/g, '',

			// wrap `not`
			/not([^)]+)/g, '!($1)',

			// interpret `all`, `portrait`, and `screen` as truthy
			/all|portrait|screen/g, 1,

			// interpret `landscape`, `print` and `speech` as falsey
			/landscape|print|speech/g, 0,

			// interpret `and`
			/\band\b/g, '&&',

			// interpret `,`
			/,/g, '||',

			// interpret `min-` as >=
			/min-([a-z-\s]+):/g, 'e.$1>=',

			// interpret `min-` as <=
			/max-([a-z-\s]+):/g, 'e.$1<=',

			// interpret others as ==
			/([a-z-\s]+):/g, 'e.$1==',

			// interpret css values
			/(\d+)([a-z]+)/g, function (match, length, unit) {
				return computeCSSValue(length, unit);
			}
		) + '}catch(e){}')({
			height: viewportHeight,
			orientation: viewportIsPortrait,
			width: viewportWidth
		});
	}
})();

Nice. Typo: on line 83 in the comment it should be 'max'.