JS: Retrieve params from the calling URL

get_params_from_url.js

export default {
  getParams() {
    const scripts  = document.getElementsByTagName('script'),
          myScript = scripts[scripts.length - 1],
          query    = myScript.src.replace(/^[^\?]+\??/, '');

    let Params = {};

    if ( !query ) { return Params } // return empty object

    const Pairs = query.split(/[;&]/);

    for ( let i = 0; i < Pairs.length; i++ ) {
      const KeyVal = Pairs[i].split('=');

      if ( !KeyVal || KeyVal.length !== 2 ) { continue }

      const key = decodeURI(KeyVal[0]),
            val = decodeURI(KeyVal[1]);

      Params[key] = val.replace(/\+/g, ' ');
    }

    return Params;
  }
};

Credit to Developing Featherweight Web Services with JavaScript