gatsby-browser.js

const injectTwitterScript = () => {
  function addJS(jsCode) {
    const s = document.createElement('script');

    s.type = 'text/javascript';
    s.innerText = jsCode;
    document.getElementsByTagName('head')[0].appendChild(s);
  }
  addJS(`
          window.twttr = (function(d, s, id) {
  var js, fjs = d.getElementsByTagName(s)[0],
    t = window.twttr || {};
  if (d.getElementById(id)) return t;
  js = d.createElement(s);
  js.id = id;
  js.src = "https://platform.twitter.com/widgets.js";
  fjs.parentNode.insertBefore(js, fjs);
  t._e = [];
  t.ready = function(f) {
    t._e.push(f);
  };
  return t;
}(document, "script", "twitter-wjs"));
`);
};

let injectedTwitterScript = false;
exports.onRouteUpdate = function ({ location }) {
  // If there's an embedded tweet, lazy-load the twitter script (if it hasn't
  // already been loaded), and then run the twitter load function.
  // console.log('load tweeter script');
  if (document.querySelector('.twitter-tweet') !== null) {
    if (!injectedTwitterScript) {
      injectTwitterScript();
      injectedTwitterScript = true;
    }

    if (
      typeof twttr !== 'undefined'
      && window.twttr.widgets
      && typeof window.twttr.widgets.load === 'function'
    ) {
      window.twttr.widgets.load();
    }
  }
};