How to add route with optional parameter after root in Node.js Express?

To add route with optional parameter after root in Node.js Express, we add a question mark after the route parameter placeholder.

For instance, we write

app.get("/api/v1/tours/:cId/:pId/:batchNo?", (req, res) => {
  console.log(req.params.cId);
  console.log(req.params.pId);
  console.log(req.params.batchNo);
});

to add the option batchNo route parameter.

We get its value from req.params.batchNo.