Source code for a simple Telegram bot on Google Cloud Functions

index.js

exports.haha = function (req, res) {
    const update = req.body;
    console.log(JSON.stringify(update));

    // update contains a message
    if (update.hasOwnProperty('message')) {
        // call the sendMessage method
        const reply = {
            method: 'sendMessage',
            chat_id: update.message.chat.id,
            text: 'haha',
        };

        return res.json(reply);
    }

    return res.sendStatus(200);
};