var express = require('express');

var app = express();

app.use(express.json()); // built-in middleware for express

app.post('/', function(request, response){
     let myJson = request.body;      // your JSON
    let myValue = request.body.myKey;    // a value from your JSON
    response.send(myJson);     // echo the result back
});

app.listen(3000);