app.js

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

const app = express();

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

app.get('/', function(req, res){
    res.sendFile(__dirname+"/signup.html");
});

app.post('/', function(req, res){
    const firstName=req.body.fname;
    const lastName=req.body.lname;
    const email=req.body.email;
    const data={
        members: [
            {
                email_address:email,
                status:"subscribed",
                merge_fields:{
                    FNAME:firstName,
                    LNAME:lastName
                }
            }
        ]
    };
    const jsonData=JSON.stringify(data);
    //replace X with X in usX of API key
    const url ="https://usX.api.mailchimp.com/3.0/lists/Uniquie ID here";
    const options={
        method:"POST",
        auth:"ArpitPandey:API Key Here"
    };
    const request=https.request(url, options, function(response){
        if(response.statusCode===200)
        {
            res.sendFile(__dirname+"/success.html");
        }
        else
        {
            res.sendFile(__dirname+"/failure.html");
        }
        response.on("data", function(data){
            console.log(JSON.parse(data));
        })
    })
    request.write(jsonData);
    request.end();
});



app.listen(3000, ()=>{
    console.log('Server started');
});