hello_bot.js

var request = require('request');

var token = 'your:token-here',
    baseUrl = 'https://api.telegram.org/bot' + token + '/';

module.exports = function(context, cb) {
    var command = context.data.message.text;
    var chat = context.data.message.chat.id;

    // intercept command /hello
    if (command.lastIndexOf('/hello', 0) === 0) {
        // response message
        sendMessage(chat, 'world!');

        // not required but...
        cb(null, {status: 'ok'});
    }
};

var sendMessage = function(chatId, message) {
    request.post(
        baseUrl + 'sendMessage',
        {
            form: {
                'chat_id': chatId,
                'text': message
            }
        }
    );
};