server.js

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


app.use(bodyParser.urlencoded({extended: false}));
app.use(bodyParser.json());
var port = process.env.PORT || 4000;

app.use(function(req, res, next) {
  // Important
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});

app.get('/', (req, res, next) => {
  res.send('reCaptcha verification...');
});

app.post('/', (req, res) => {
  if(
    req.body.captcha === undefined ||
    req.body.captcha === '' ||
    req.body.captcha === null
  ){
    return res.json({"success": false, "msg":"Please select captcha"});
  }

  // Secret Key from Heroku Config Variable 'RECAPTCHA_SECRET'
  const secretKey = process.env.RECAPTCHA_SECRET;

  // Google's verification URL: https://developers.google.com/recaptcha/docs/verify
  const verifyUrl = `https://google.com/recaptcha/api/siteverify?secret=${secretKey}&response=${req.body.captcha}&remoteip=${req.connection.remoteAddress}`;

  // Make Request To VerifyURL
  request(verifyUrl, (err, response, body) => {
    body = JSON.parse(body);

    // If Not Successful
    if(body.success !== undefined && !body.success){
      return res.json({"success": false, "msg":"Failed captcha verification from live server"});
    }

    //If Successful
    return res.json({"success": true, "msg":"reCaptcha passed from live server"});
  });
});


app.listen(port, function () {
  console.log('App listening on port ' + port);
});