URL Encoding

The first issue (I guess?) in the code I see is that you're using & instead of ? to start the query parameters; we use & to separate key value pairs (like foo=bar&baz=hello). So, you might want to check that once.

If you change the & to a ?, you can access it using req.query.<objectName>.

Other Solutions

I also just your edit, and for that to work we can work with /house/:id/:country/:stateAndZip we need to make a few changes.

I would probably use this approach:

const { stateAndZip } = req.params;
const [ state, zipCode ] = stateAndZip.split( '&' );

// Here, state contains 'ny' and `zipCode` is of the work `zipcode=XXXXX`. 
const [ , formattedZipCode ] = zipCode.split( '=' ); // Or use https://nodejs.org/api/querystring.html

// formattedZipCode is XXXXX.

There are a few problems with this solution; the first one being that this assumes the zipcode is the first argument after &. If you want a more generic way of doing it, please let me know.

A Better Solution

Taking the solution from above and assuming we have an unordered list where zipcode can be anywhere, we can do the following:

const qs = require( 'querystring' );

const { stateAndZip } = req.params;
const [ state, queryParams ] = stateAndZip.split( '&' );
const decodedQueryParams = qs.parse( queryParams );

// decodedQueryParams will be an object with the property `zipcode`.

One issue here is that we may have an ampersand (&) in the URL itself, you can take this solution a step further by assuming that all state names in their abbreviated form are only 2 characters and read till the &, and parse out the remaining string using querystring.

As mentioned, your requirement is a bit strange. However, expressjs router's path definition is very elastic (look for Route paths section under official documentation). You can define a route with your pattern like this:

/:id/:country/:state&zipcode=:zipcode

Fast testing

Use Express Route Tester, put /house/:id/:country/:state&zipcode=:zipcode in Route field and /house/1/us/ny&zipcode=12345 in Path field.

Full example

import * as express from 'express';

const express = require("express");
const app = express();
const houseRouter = express.Router();
houseRouter.get("/:id/:country/:state&zipcode=:zipcode", (req) => {
  console.log(req.params);
});
app.use('/house', houseRouter);
app.listen(3000);

To test, call http://localhost:3000/house/1/us/ny&zipcode=12345 from postman/browser.

Console would log:

{ id: '1', country: 'us', state: 'ny', zipcode: '12345' }

The endpoint should be /house/1/us/ny?zipcode=12345 and then req.query.zipcode will have the zipcode value. ? instead of &.

When /house/1/us/ny&zipcode=12345 is used, req.params consider ny&zipcode=12345 as the value for the key state. ? ends the endpoint and begins the query parameters.