How to solve POST request req.body is empty?

const express = require('express');

const app = express();

app.post('/add', (req, res) =>{
    const {a, b} = req.body; // TypeError: Cannot destructure property 'a' of 'req.body' as it is undefined.
    const ret = parseInt(a) + parseInt(b);
    res.send(`${a} + ${b} = ${ret}`);
});

app.listen(3000, () => {
    console.log(`Example app listening at http://localhost:3000`);
});

Install bodyParser to parse body content

1. npm instll body-parser
2. Use bodyParser.json and bodyParser.urlencoded as middleware.

   const express = require('express');
   const bodyParser = require('body-parser')
   
   const app = express();
   app.use(bodyParser.urlencoded({ extended:true }));
   app.use(bodyParser.json());
   
   app.post('/add', (req, res) =>{
       const {a, b} = req.body; // now you can get your request data here
       const ret = parseInt(a) + parseInt(b);
       res.send(`${a} + ${b} = ${ret}`);
   });
   
   app.listen(3000, () => {
       console.log(`Example app listening at http://localhost:3000`);
   });