I followed the best solution below:
can’t watch multiple files with json-server

db.js

var firstRoute  = require('./jsonfile1.json');
var secondRoute = require('./jsonfile2.json');

module.exports = function() {
  return {
    firstRoute  : "/people",
    secondRoute : "/dates"
  }
}

server.js

var jsonServer  = require('json-server')
var server      = jsonServer.create()
var router      = jsonServer.router(require('./db.js')())
var middlewares = jsonServer.defaults()

server.use(middlewares)
server.use(router)
server.listen(3000, function () {
console.log('JSON Server is running')
})

Then I ran node server.js

I get this error:
Error: Type of “firstRoute” (string is not supported. Use objects or arrays of objects

Sorry, I am not too familiar with backend and wanted to use json-server to practice. What is wrong here?