json-server: Default JSON for non-matching route - json-server

Question

I want to fake a login API with the route /api/login/:userName/:password that would return { "success": false, "userName": "", "password": "" } in case userName or password is not found in the database. How can I achieve this with json-server?
So far I have this database JSON:
{
"login": [
{ "success": true, "userName": "zaphod", "password": "galaxy" }
],
"invalidLogin": [
{ "success": false, "userName": "", "password": "" }
]
}
invalidLogin is currently not used and should be used for every login route with unknown userName or password.
This is my server.js:
const jsonServer = require('json-server');
const server = jsonServer.create();
const router = jsonServer.router('db.json');
const middlewares = jsonServer.defaults();
server.use(middlewares);
// Rewrite rules
server.use(jsonServer.rewriter({
'/login/:userName/:password': "/login?userName=:userName&password=:password"
}))
server.use('/api', router);
server.listen(3001, () => {
console.log('JSON Server is running')
});

Answer 1

You can achieve something like this using router.render function:
router.render = (req, res, next) => {
if (req.path === '/login') {
if (res.locals.data.length !== 0) {
res.jsonp(res.locals.data);
} else {
res.jsonp([
{ "success": false, "userName": "", "password": "" }
])
}
} else {
res.jsonp(res.locals.data);
}
}
Basically this router code will check if there are non-empty response to /login/.../... and afterwards replace it with error JSON on empty login request. You can upgrade this mock's logic further.
Aforementioned code can be placed after rewrite rules in server.js (there was a minor error in your code, you have to write it with api, reference issue):
server.use('/api', jsonServer.rewriter({
"/login/:userName/:password": "/login?userName=:userName&password=:password",
}))