Exemplo simples de api com express nodejs

index.js

/*
  yarn add express body-parser cors
  node index.js
*/

const express     = require('express')
const bodyParser  = require('body-parser')
const app         = express()
const cors        = require('cors');

app.use(cors());
app.use(bodyParser.json())
app.use(bodyParser.urlencoded({extended:true}))

app.get('/api', (req, res) => {
  const {query} = req
  const json = {}
  for (const [key, value] of Object.entries(query)) {
    json[key] = value
  }
  res.json({ data: json })
})

app.get('/api/user/:id', (req, res) => {
  const {params} = req
  console.log(params)
  res.json({ data: params })
})

app.post('/api', (req, res) => {
  const {body} = req
  const json = {}
  for (const [key, value] of Object.entries(body)) {
    json[key] = value
  }
  res.json({ data: json })
})

app.listen(5000)

test.txt

Teste a api via curl

//fazendo um get /api
curl -X GET 'http://localhost:5000/api?username=code365&website=code365.web.app'

//fazendo um post /api com json
curl -X POST 'http://localhost:5000/api' -H 'Content-Type: application/json' -d '{"username":"code365","website":"code365.web.app"}'

//fazendo um get /api/user/:id
curl -X GET 'http://localhost:5000/api/user/1'