Google Tag Manager script unminified

gtm-unminified.js

window['dataLayer'] = window['dataLayer'] || [];

window['dataLayer'].push({
  'gtm.start': new Date().getTime(),
  event: 'gtm.js'
});

const firstScriptElement = document.getElementsByTagName('script')[0];

const scriptElement = document.createElement('script')
scriptElement.async = true;
scriptElement.src = 'https://www.googletagmanager.com/gtm.js?id=GTM-1234567';

firstScriptElement.parentNode.insertBefore(scriptElement, firstScriptElement);