JS dodaj dolne cięcie do URL (jeśli nie obecne)

var lastChar = url.substr(-1); // Selects the last character
if (lastChar != '/') {         // If the last character is not a slash
   url = url + '/';            // Append a slash to it.
}

// The temporary variable name can be omitted, and directly embedded in the assertion:

if (url.substr(-1) != '/') url += '/';

// Since the goal is changing the url with a one-liner, the following solution can also be used:

url = url.replace(/\/?$/, '/');
// If the trailing slash exists, it is replaced with /.
// If the trailing slash does not exist, a / is appended to the end (to be exact: The trailing anchor is replaced with /).
Ill Iguana