Dynamic loading of external CSS and Javascript files. 287 bytes minified.

loader.js

/**
* Dynamic loading of external CSS and Javascript files. 287 bytes minified. Usage:
* load(['some.css', 'lib.js'], function() { console.log('loaded!') });
*/

var load = function (urls, done) {
  var doc = document;
  var cnt = urls.length;
  var head = doc.getElementsByTagName('head')[0];
  var onload = function () {
    if (--cnt === 0) done();
  };
  urls.forEach(function (url) {
    var n;
    if (url.substr(-4) === '.css') {
      n = doc.createElement('link');
      n.rel = 'stylesheet';
      n.href = url;      
    } else {
      n = doc.createElement('script');
      n.src = url;
    }
    n.onload = onload;
    head.appendChild(n);
  });
};