.js

function validate(schema) {
  return function (req, res, next) {
    // assuming joi callback style validation
    schema.validate(req.params, schema, function (err, coercedParams) {
      if (err) { next(err); return; } // if you want to handle errors with middleware
      // if (err) { req.params = null; req.validationError = err; } // if you want to handle it in your route
      else { req.params = coercedParams; } // replacing req.params with the validated/coerced version
      next();
    });
  };
}

// testing it
var validateMiddleware = validate(someSampleSchema);
var req = { params: { foo: 'bar' } };
validateMiddleware(req, res, function (validatedReq) {
  // assert that validatedReq is shaped as you expect
});