A simple function with no dependencies to load external javascripts. Features include:- Loading multiple scripts at once;- Callback function to execute once all scripts have loaded;- Optionally load scripts asynchronously;- Optionally define a DOM object where scripts will be inserted.

script-loader.js

/**
 * Snippet function to load external scripts.
 * @param {[String, Array]} sources Array of sources to load.
 * @param {[Functon]} callback      A callback to run when all scripts have loaded.
 * @param {[Boolean]} aasync        Whether sources should be loaded
 *                                  asynchronously or not.
 * @param {[Object]} appendTo       Optionally provide a DOM object to append
 *                                  the script tags to.
 */
function scriptLoader(sources, callback, async, appendTo) {

  // Parse variables.
  sources  = typeof sources == 'string' ? [sources] : sources || [];
  async    = typeof async == 'undefined' ? true : async;
  appendTo = appendTo || document.body;

  var toLoad = !async ? sources.splice(0, 1) : sources;
  var scriptTag = null;
  var i = l = 0; // Incrementals.

  do {

    // Terminate when iterator exceeds amount of items.
    if (!toLoad[i]) return callback && callback(appendTo);

    // Create script tag.
    scriptTag = document.createElement('SCRIPT');
    scriptTag.src = toLoad[i];
    scriptTag.onload = function() {
      var run = !async;
      if (async && ++l == sources.length) {
        run = true;
        sources = [];
      }
      run && appendScripts(sources, callback, true, appendTo);
    }

    // Place script on document to load it.
    appendTo.appendChild(scriptTag);

  } while (++i < toLoad.length);
}