function newUrlAttr(url, name, val, useDoubleEncoding) { // the double backslash escapes the backslash so we get '?' for the regexp var ques = '?'; var esc_ques = '\?'; var amp = '&'; var eq = '='; // double encodings: & %2526 ? %253F = %253D, // don't need to escape the ? for regexp if (useDoubleEncoding) { ques = '%253F'; esc_ques = '%253F'; amp = '%2526'; eq = '%253D'; } var exp = new RegExp('('+name+eq+'.*?)'+amp); // /(name=val)&/ - mid url if (url.match(exp)) { var existing = url.match(exp)[1]; } else { exp = new RegExp('('+name+eq+'.*)'); // /(name=val)/ - end of the url if (url.match(exp)) { var existing = url.match(exp)[1]; } } if (existing) { url = url.replace(existing, name+eq+val); } else { var exp1 = new RegExp(esc_ques); // url a '?' should have some params var exp2 = new RegExp(esc_ques+'$'); // url end