How to add a query string to req.url in Express?

Question

I want to add a string to a req.url in Express. The string looks like this:

?id=someID&product=bag

I don't have an access to client html or server. All I get from client it's just a GET request without any parameters. So I tried to make middleware which would add query string and then I will parse it like always. The idea was:

// Middleware

const addQuery = (req, res, next) => {
    req.url = req.url + `?id=someID&product=bag`;
    next();
}

And then in request handler:

router.get('/', addQuery, (req, res) => {
    console.log(req.query.id);
    console.log(req.query.product);
});

But it gives me undefined. I can't use any client side js and I can't use server side coding. Not my origin sends me this request.

So how to add query string to express request and then successfully parse it?

Answer 1

express appears to export a middleware called query that it uses to parse query strings. Because this middleware is typically called early in the request flow, adding a query string to req.url happens "too late".

Here's a workaround that appears to work:

const addQuery = (req, res, next) => {
  req.url   = req.url + `?id=someID&product=bag`;
  req.query = null; // if this isn't added, the `query` middleware
                    // will assume the query string is already parsed
  next();
}

app.get('/', addQuery, express.query(), (req, res) => {
  ...
});

EDIT: as @wlh rightfully suggests, addQuery could also modify req.query directly:

const addQuery = (req, res, next) => {
  req.query.id      = 'someID';
  req.query.product = 'bag';
  next();
}

This should work pretty much the same, but much cleaner.