run callback when browser environment ready - run immediately outside of browser

runWhenBrowserEnvReady.js

const isRunningInBrowser = typeof window !== 'undefined';

function runWhenBrowserEnvReady(fn) {
  if (isRunningInBrowser) {
    const doc = document;
    doc.readyState[0] === 'l' ? doc.addEventListener('DOMContentLoaded', fn) : fn();
  } else {
    fn();
  }
}