app.js

const { Client, NoAuth } = require('whatsapp-web.js');
const qrcode = require('qrcode-terminal');
const fs = require('fs');
const csv = require('csv-parser');

const message = fs.readFileSync("./message.txt", {encoding: 'utf-8'});
const contacts = [];

fs.createReadStream('contacts.csv')
.pipe(csv())
.on('data', function(data) {
    try {
        contacts.push(data.number); 
    } catch(err) {
        console.error(err);
    }
})
.on('end', () => {
    // console.log(contacts);
});

let counter = { fails: 0, success: 0 }

/*
const SESSION_FILE_PATH = './whatsapp-session.json';
let sessionCfg;
if (fs.existsSync(SESSION_FILE_PATH)) {
    sessionCfg = require(SESSION_FILE_PATH);
}

const client = new Client({
    session: sessionCfg
});
*/

// equivalent to
const client = new Client({
    authStrategy: new NoAuth()
});

client.initialize();

client.on('qr', (qr) => {
    qrcode.generate(qr, { small: true });
});

/*
client.on('authenticated', (session) => {
    console.log('AUTHENTICATED', session);
    sessionCfg = session;
    fs.writeFile(SESSION_FILE_PATH, JSON.stringify(session), function (err) {
        if (err) {
            console.error(err);
        }
    });
});
*/

client.on('auth_failure', msg => {
    // Fired if session restore was unsuccessfull
    console.error('AUTHENTICATION FAILURE', msg);
});

client.on('ready', () => {
    console.log('Client is ready!');
    deploy_all();
});

client.on('disconnected', (reason) => {
    console.log('Client was logged out', reason);
});

async function deploy_all() {
    for (const contact of contacts) {
        const final_number = (contact.length > 10) ? `${contact}@c.us` : `91${contact}@c.us`;
        const isRegistered = await client.isRegisteredUser(final_number);
        if (isRegistered) {
            const msg = await client.sendMessage(final_number, message);
            console.log(`${contact} Sent`);
            counter.success++;
            /*
            deleteChat(final_number)
            .then((res) => console.log(res)) // contains ["successfuly deleted"]
            .catch((err) => console.log(err))// contains ["something went wrong", "do not have chat history"]
            */
        } else {
            console.log(`${contact} Failed`);
            counter.fails++;
        }
    }
    console.log(`Result: ${counter.success} sent, ${counter.fails} failed`);
}

async function deleteChat(phoneNumber) {
    return new Promise((resolve, reject) => {
        client.getChatById(phoneNumber).then((chat) => {
            // console.log("Chat information = ", chat)
            chat.delete().then((deleteRes) => {
                if(deleteRes) 
                    resolve(`successfuly deleted`)
                else 
                    reject("something went wrong")
            })
        }).catch((err) => {
            if(err.message.includes("Cannot read property 'serialize' of undefined"))
                reject(`do not have chat history`)
            // can handle other error messages...     
        })
    })
}