How to dynamically load JavaScript and CSS

gistfile1.js

var OptaAshes = {
    scriptBase: "widget/",
    require:function(s) {
        try{
            // inserting via DOM fails in Safari 2.0, so brute force approach
            if(s.type == "text/javascript") {
                document.write('<script type="text/javascript" src="'+s.url+'"><\/script>');
            } else {
                document.write('<link rel="stylesheet" href="'+ s.url +'" />');
            }
        } catch(e) {
            // for xhtml+xml served content, fall back to DOM methods
            if(s.type == "text/javascript") {
                var script = document.createElement('script');
                script.type = 'text/javascript';
                script.src = s.url;
                document.getElementsByTagName('head')[0].appendChild(script);
            } else {
                var style = document.createElement('link');
                style.rel = 'stylesheet';
                style.href = s.url;
                document.getElementsByTagName('head')[0].appendChild(style);
            }
        }
    },
    
    load:function() {
        
        var scripts = document.getElementsByTagName("script");
        var script;
        var scriptBase = this.scriptBase;
        for(var i = 0, l = scripts.length; i < l; ++i) {
            script = scripts[i];
            if( script.src.indexOf("/opta.cricket.js") != -1 )
            {
                scriptBase = script.src.replace("/opta.cricket.js", "/");
            }
        }

        
        if(typeof jQuery == 'undefined') {
            OptaAshes.require({"type":"text/javascript", "url":scriptBase+"jquery-1.4.4.min.js"});
        }
        
        var script_urls = [
             {"type":"text/css", "url":scriptBase+"default.css"},
            // {"type":"text/css", "url":this.scriptBase+"red.css"},
            {"type":"text/javascript", "url":scriptBase+"jquery-ui-1.8.6.custom.min.js"},
            {"type":"text/javascript", "url":"http://js.kwwika.com/beta/api.js"},
            {"type":"text/javascript", "url":scriptBase+"date.js"},
            {"type":"text/javascript", "url":scriptBase+"cricket.js"}
        ];
        
        for(s in script_urls) {
            OptaAshes.require(script_urls[s]);
        }
    }
}

OptaAshes.load();