Load Javascript file after page load

loadJS.coffee

loadJS = (src, callback = new Object(), doCallbackOnError = true) ->
  ###
  # Load a new javascript file
  #
  # If it's already been loaded, jump straight to the callback
  #
  # @param string src The source URL of the file
  # @param function callback Function to execute after the script has
  #                          been loaded
  # @param bool doCallbackOnError Should the callback be executed if
  #                               loading the script produces an error?
  ###
  if $("script[src='#{src}']").exists()
    if typeof callback is "function"
      try
        callback()
      catch e
        console.error "Script is already loaded, but there was an error executing the callback function - #{e.message}"
    # Whether or not there was a callback, end the script
    return true
  # Create a new DOM selement
  s = document.createElement("script")
  # Set all the attributes. We can be a bit redundant about this
  s.setAttribute("src",src)
  s.setAttribute("async","async")
  s.setAttribute("type","text/javascript")
  s.src = src
  s.async = true
  # Onload function
  onLoadFunction = ->
    state = s.readyState
    try
      if not callback.done and (not state or /loaded|complete/.test(state))
        callback.done = true
        if typeof callback is "function"
          try
            callback()
          catch e
            console.error "Postload callback error - #{e.message}"
    catch e
      console.error "Onload error - #{e.message}"
  # Error function
  errorFunction = ->
    console.warn "There may have been a problem loading #{src}"
    try
      unless callback.done
        callback.done = true
        if typeof callback is "function" and doCallbackOnError
          try
            callback()
          catch e
            console.error "Post error callback error - #{e.message}"
    catch e
      console.error "There was an error in the error handler! #{e.message}"
  # Set the attributes
  s.setAttribute("onload",onLoadFunction)
  s.setAttribute("onreadystate",onLoadFunction)
  s.setAttribute("onerror",errorFunction)
  s.onload = s.onreadystate = onLoadFunction
  s.onerror = errorFunction
  document.getElementsByTagName('head')[0].appendChild(s)
  true

loadJS.js

loadJS = function(src, callback, doCallbackOnError) {
  var e, errorFunction, onLoadFunction, s;
  if (callback == null) {
    callback = new Object();
  }
  if (doCallbackOnError == null) {
    doCallbackOnError = true;
  }

  /*
   * Load a new javascript file
   *
   * If it's already been loaded, jump straight to the callback
   *
   * @param string src The source URL of the file
   * @param function callback Function to execute after the script has
   *                          been loaded
   * @param bool doCallbackOnError Should the callback be executed if
   *                               loading the script produces an error?
   */
  if ($("script[src='" + src + "']").exists()) {
    if (typeof callback === "function") {
      try {
        callback();
      } catch (_error) {
        e = _error;
        console.error("Script is already loaded, but there was an error executing the callback function - " + e.message);
      }
    }
    return true;
  }
  s = document.createElement("script");
  s.setAttribute("src", src);
  s.setAttribute("async", "async");
  s.setAttribute("type", "text/javascript");
  s.src = src;
  s.async = true;
  onLoadFunction = function() {
    var state;
    state = s.readyState;
    try {
      if (!callback.done && (!state || /loaded|complete/.test(state))) {
        callback.done = true;
        if (typeof callback === "function") {
          try {
            return callback();
          } catch (_error) {
            e = _error;
            return console.error("Postload callback error - " + e.message);
          }
        }
      }
    } catch (_error) {
      e = _error;
      return console.error("Onload error - " + e.message);
    }
  };
  errorFunction = function() {
    console.warn("There may have been a problem loading " + src);
    try {
      if (!callback.done) {
        callback.done = true;
        if (typeof callback === "function" && doCallbackOnError) {
          try {
            return callback();
          } catch (_error) {
            e = _error;
            return console.error("Post error callback error - " + e.message);
          }
        }
      }
    } catch (_error) {
      e = _error;
      return console.error("There was an error in the error handler! " + e.message);
    }
  };
  s.setAttribute("onload", onLoadFunction);
  s.setAttribute("onreadystate", onLoadFunction);
  s.setAttribute("onerror", errorFunction);
  s.onload = s.onreadystate = onLoadFunction;
  s.onerror = errorFunction;
  document.getElementsByTagName('head')[0].appendChild(s);
  return true;
};