Helper functions for extracting the App Web and Host URL - JavaScript (es6)

Utils.js

function getDocumentQueryStrings() {
  const sections = document.URL.split('?');

  return sections.length > 1 ? sections[1].split('&') : [];
}

function S4() {
  return (((1 + Math.random())*0x10000)|0).toString(16).substring(1); 
}

module.exports = {
  baseUrl(host) {
    let hostname = host;

    if (hostname && hostname.match(/[-][\w]+[-]/g)) {
      hostname = hostname.match(/[-][\w]+[-]/g)[0];
      hostname = hostname.substring(1, hostname.length - 1);
      hostname = `${window.location.protocol}//twad${hostname}.sharepoint.com${(window.location.port ? ':' + window.location.port : '')}`;
    }
    return hostname;
  },
  baseAssetSiteUrl() {
    return `${this.baseUrl(window.location.origin)}/sites/`;
  },
  getGuid() {
    return (S4() + S4() + "-" + S4() + "-4" + S4().substr(0,3) + "-" + S4() + "-" + S4() + S4() + S4()).toLowerCase();
  },
  getQueryStringParameter(param) {
    const el = getDocumentQueryStrings().filter(keyPair => keyPair.split('=')[0] === param);

    return el.length > 0 ? window.decodeURIComponent(el[0].split('=')[1]) : null;
  },
  getSpContaxtUrlParams() {
    return {
      hostWebUrl: window.decodeURIComponent(this.getQueryStringParameter('SPHostUrl')),
      appWebUrl: window.decodeURIComponent(this.getQueryStringParameter('SPAppWebUrl')),
      spLanguage: window.decodeURIComponent(this.getQueryStringParameter('SPLanguage'))
    };
  }
};