Use node-gcm using npm

notify.js

var gcm = require('node-gcm');

var notify     = exports;

notify.send = function(msg, reg_id) {
    var message = new gcm.Message();
    message.addData('msg', msg);
    // get token here
    // TODO
    //var regTokens = ['APA91bFiJx52Iq2_LwyXPUWeO0Vg-9DmrWW6E6BmjwNUtTIrWRNOIDzaCmOidzndjZE3zWvL248GtqBYIV7YsD9q37M0urFz3FD6DvYkOaVqJqV3V9CciPletqzbJqvEm-54cpwMNcxP'];
    var regTokens = [reg_id];
    
    // Set up the sender with you API key
    var sender = new gcm.Sender('API KEY');
    
    // Now the sender can be used to send messages
    sender.send(message, { registrationTokens: regTokens }, function (err, response) {
        if(err) console.error("Error"+err);
        else    console.log("Response"+response);
    });
}

notify(null, null);