npm install express-api-version-manager

    app.use('/api/:apiVersion', apiVersionManager({
      apiVersionParamName: 'apiVersion',
      versions: {
        v1: {
          router: routerApiV1
        },
        v2: {
          router: routerApiV2
        },
        v3: {
          router: routerApiV3
        }
      }
    }));

const express = require('express');
const apiVersionManager = require('./../index');
const app = express();

const routerApiV1 = express.Router();

const routerApiV2 = express.Router();

const routerApiV3 = express.Router();



app.use('/api/:apiVersion', apiVersionManager({
  apiVersionParamName: 'apiVersion',
  versions: {
    v1: {
      router: routerApiV1
    },
    v2: {
      router: routerApiV2
    },
    v3: {
      router: routerApiV3
    }
  }
}));
//call api/v1/user response -> user1
routerApiV1.get('/user', (req, res) => res.send('user1'));
//call api/v2/user response -> user2
routerApiV2.get('/user', (req, res) => res.send('user2'));
//call api/v3/user response -> user3
routerApiV3.get('/user', (req, res) => res.send('user3'));



//call api/v1/admin response -> admin
//call api/v2/admin response -> admin
//call api/v3/admin response -> admin
//because v2 and v3 inherit from v1
routerApiV1.get('/admin', (req, res) => res.send('admin'));