JavaScript -  Get URL QueryString Parameters - ES6 Features

getUrlParams.es6.js

/**
 * Accepts either a URL or querystring and returns an object associating 
 * each querystring parameter to its value. 
 *
 * Returns an empty object if no querystring parameters found.
 */
function getUrlParams(urlOrQueryString) {
  if ((i = urlOrQueryString.indexOf('?')) >= 0) {
    const queryString = urlOrQueryString.substring(i+1);
    if (queryString) {
      return _mapUrlParams(queryString);
    } 
  }
  
  return {};
}

/**
 * Helper function for `getUrlParams()`
 * Builds the querystring parameter to value object map.
 *
 * @param queryString {string} - The full querystring, without the leading '?'.
 */
function _mapUrlParams(queryString) {
  return queryString    
    .split('&') 
    .reduce((urlParams, urlParam) => {
      const [key, value] = urlParam.split('=');
      if (Number.isInteger(parseInt(value)) && parseInt(value) == value) {
        return {...urlParams, [key]: parseInt(value)}
      } else {
        return {...urlParams, [key]: decodeURI(value)}
      }
    }, {});
}