Cannot pass optional parameter to expression after defining it

Question

I have my optional parameter defined using my function parambelow, but when I try to pass the postman in the optional parameter, I get a Reference Error 'off' is not defined. I cannot figure out how to use the value that I pass for the parameter in the second function below, and I assume that my misuse of this is what causes the error. I am trying to determine my parameter in the first function.

router.param('off', function(req, res, next, off){
  req.offset = off;
  next();
});

I define my route with an optional parameter here

router.get('/messages/:offset',  function(request, res) {
    ctxioClient.accounts(ID).messages().get({limit: 100, offset: off},
    function ( err, response) {

    )};
)};

Answer 1

Additional parameters are defined using ?

router.get('/messages/:offset?',  function(request, res) {
  var offset = req.params.offset || 0;
  // make 0 if no offset is present
  ctxioClient.accounts(ID).messages().get({limit: 100, offset: offset},
  function ( err, response) {

  )};
)};