parseUrlParams() - Parses URL parameters.

parseUrlParams.js

  /**
   * @param {string} url
   *   A URL or a query string starting with a question mark that will be parsed.
   * @return {{
   *   first: {[k: string]: (boolean|number|string|undefined)};
   *   multi: {[k: string]: (boolean|number|string|undefined)[]};
   *   last: {[k: string]: (boolean|number|string|undefined)};
   * }}
   *   An object containing the URL parameters.  The `first` property will be an
   *   object where a key corresponds to a URL parameter name and the value
   *   corresponds to the first value for that key.  The `multi` property will be
   *   an object where a key corresponds to a URL parameter name and the value is
   *   an array containing all of the values for that key.  The `last` property
   *   will be an object where a key corresponds to a URL parameter name and the
   *   value corresponds to the last value for that key.  The values `"on"`,
   *   `"yes"` and `"true"` will be interpreted as `true`.  The values `"off"`,
   *   `"no"` and `"false"` will be interpreted as `false`. Values that look like
   *   numbers will be interpreted as numbers.
   */
  function parseUrlParams(url) {
    const result = {first: {}, multi: {}, last: {}};
    url = url.replace(/\+/g, ' ').replace(/^[^?#]*(\?)|#[^]*$/g, '$1');
    const rgxIter = /\?[^?]*/.exec(url)?.[0]?.matchAll(/[?&]([^=&]+)(?:=([^&]*))?/g);
    for (let [_, key, value] of rgxIter) {
      // Decodes the key and the value.
      key = decodeURIComponent(key);
      value = value && decodeURIComponent(value);
      // Test if the value is a boolean.
      const m = /^(?:(on|yes|true)|off|no|false)$/.exec(value);
      if (m) {
        value = !!m[1];
      }
      // Test if the value is a number.
      else if (/^-?(?:(?:(?:\d+|\d+\.\d+|\.\d+)(?:e-?\d+)?)|Infinity)$/.test(value)) {
        let num = +value;
        // If value was turned into a number other than NaN use it as the value.
        if (num === num) value = num;
      }
      // If the key has not yet been seen go ahead and define it for `first` and
      // start an array for `multi`.
      if (!result.hasOwnProperty.call(result.last, key)) {
        result.first[key] = value;
        result.multi[key] = [];
      }
      result.last[key] = value;
      result.multi[key].push(value);
    }
    return result;
  }