Express.js req, res

app.post("/yourPageUrl", (req, res) => {
var your codes goes here
//there is something have to remember is that req is you get the data from the form. (i.e in CI4 $this->request->getPost('name') you request it), and res is when client visit the url, then you response with something else. req comes first and then res. Do not fuck it up.
})

const express = require('express')
const bodyParser = require("body-parser");
const app = express();
const port = 3000

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

app.get('/', (req, res) => {
  res.send('Hello World!')
})

app.get("/calculator", (req, res) => {
  res.sendFile(__dirname + "/calculator.html");
})

app.post("/",(req, res) => {

  
  var number1 = Number(req.body.num1);
  var number2 =Number(req.body.num2);



  var result = number1 + number2;

  res.send("The result of the calculation is " + result);
})

app.get("/bmialculator", (req, res) => {
  res.sendFile(__dirname + "/bmiCalculator.html");
})

app.post("/calculated", (req, res) => {
  var weight = req.body.weight;
  var height = req.body.height;

  var bmi = weight / (height * height);
  res.send("Your bmi is " + bmi);

})  


app.listen(port, () => {
  console.log(`Example app listening on port ${port}`)
})