getParam(get_param, url = window.location.href) {
        const params = this.getParams(url);
        if (params === undefined) {
            return undefined;
        }
        return params[get_param];
    }
Get the value of a URI query HTTP GET param (?param=val) from current URL or string
If param has [] in name, returns Array
If param not set returns undefined
If param exists but has no value returns empty string ''

@param  {String}                  get_param  The field to get the value of
@param  {String?}                 url        The URL to get the value from, default current URL
@return {String|Array|undefined}             The GET param value or undefined