Factory to inject non-Angular library to the application, here is Lodash for example.

lodash.factory.js

(function () {
  angular
    .module('shared.factories')
    .factory('_', LodashFactory);

  LodashFactory.$inject = ['$window', '$state'];
  function LodashFactory($window, $state) {
    if(!$window._){
      var lodashCdnUrl = 'https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js';
      loadScript(lodashCdnUrl, function () {
        return $window._;
      }, function () {
        $state.to('error', {code: 424});
      });
    }
    return $window._;
  }

  function loadScript(url, successCallback, errorCallback) {
    var script = document.createElement("script");
    script.type = "text/javascript";
    lodashScript.async = false;

    if (script.readyState) { //IE
      script.onreadystatechange = function () {
        if (script.readyState == "loaded" || script.readyState == "complete") {
          script.onreadystatechange = null;
          successCallback();
        } else {
          errorCallback();
        }
      };
    } else { //Others
      script.onload = successCallback;
      script.onerror = errorCallback;
    }

    script.src = url;
    (document.getElementsByTagName('head')[0]
    || document.getElementsByTagName('body')[0]).appendChild(script);
  }
})();