Include javascript and css dynamically

Some script I must post here in case of my bad memory. Maybe useful for my blog visitors.

 1 var getHead = function() {
 2                 return document.getElementsByTagName("head")[0];
 3             };
 4             var includeJavascriptFile = function(url) {
 5                 if (document.body == null) {
 6                     document.write("<script src='" + url + "' type='text/javascript'></script>");
 7                 } else {
 8                     var script = document.createElement("script");
 9                     script.type = "text/javascript";
10                     script.language = "JavaScript";
11                     script.src = url;
12                     getHead().appendChild(script);
13                 }
14             };
15             var includeCssFile = function(url) {
16                 if (document.body == null) {
17                     document.write("<link rel='stylesheet' href='" + url + "' type='text/css'/>");
18                 } else {
19                     var link = document.createElement("link");
20                     link.setAttribute("rel", "stylesheet");
21                     link.setAttribute("type", "text/css");
22                     link.setAttribute("href", url);
23                     getHead().appendChild(link);
24                 }
25             }