dynamic-script-import.js

var waitForDOM = function (callback) {
  document.addEventListener("DOMContentLoaded", function () {
    setTimeout(function () {
      callback();
    }, 5000);
  });
};

var waitFor = function (callbackValue, callback) {
  if (callbackValue()) {
    callback();
  } else {
    setTimeout(function () {
      waitFor(function () {
        return callbackValue();
      }, callback);
    }, 100);
  }
};

var waitForGlobal = function (key, callback) {
  waitFor(function () {
    return window[key];
  }, callback);
};

var importScript = function importScript(src, callback) {
  var script = document.createElement("script");
  script.src = src;
  script.defer = true;

  if (typeof callback === "function") {
    script.onload = callback;
  }

  document.getElementsByTagName("head")[0].appendChild(script);
};