Add a CSS stylesheet to the head of a document

includeCSS.js

$.extend({
  includeCss: function(cssLink, isPrint, callbackFn) {
		var $head = $("head");
		//Make sure it's a valid string and not already included in the head
		if (typeof cssLink === "string" && cssLink.length > 1 && $head.find("link[href='" + cssLink + "']").length <= 0) {
			//Create a new link element
			var $newLinkTag;
			var mediaType = (isPrint) ? 'print' : 'all';
			
			//Needed for IE8 and lower
			if (typeof document.createStyleSheet !== "undefined") {
				document.createStyleSheet(cssLink);
				$newLinkTag = $head.find("link[href='" + cssLink + "']");
				$newLinkTag.attr({
					"media": mediaType,
					"data-dynamic": "true"
				});
			} else {
				//Add the CSS file to the head
				$newLinkTag = $("<link rel='stylesheet' type='text/css' data-dynamic='true' media='" + mediaType + "' href='" + cssLink + "' />");
				$head.append($newLinkTag);
			}

			//Convert the 2nd param to the callback if it's a function and the 3rd is undefined
			if (typeof callbackFn === "undefined" && $.isFunction(isPrint)) callbackFn = isPrint;

			//Run the callback
			if ($.isFunction(callbackFn)) callbackFn($newLinkTag);
		}
	}
});

Usage:

Simple: $.includeCss('link/to/file.css');
will add <link href=​"link/to/file.css" rel=​"stylesheet" media=​"all" type=​"text/​css">​ to the document head.

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Make it a print stylesheet: $.includeCss('link/to/file.css',true);
will add <link href=​"link/to/file.css" rel=​"stylesheet" media=​"print" type=​"text/​css"> to the document head.

---

Add a callback function: $.includeCss('link/to/file.css',true,function(css){ console.log("I'm Done!", css); });
or, skip the 2nd param: $.includeCss('link/to/file.css',function(css){ console.log("I'm Done!", css); });

the paramaeter passed to the callback function will return the newly created link element in the head - just in case that's needed!