node-gcm

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

// Set up the sender with your GCM/FCM API key (declare this once for multiple messages)
var sender = new gcm.Sender('YOUR_API_KEY_HERE');

// Prepare a message to be sent
var message = new gcm.Message({
    data: { key1: 'msg1' }
});

// Specify which registration IDs to deliver the message to
var regTokens = ['YOUR_REG_TOKEN_HERE'];

// Actually send the message
sender.send(message, { registrationTokens: regTokens }, function (err, response) {
	if (err) console.error(err);
	else console.log(response);
});

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

// Create a message
// ... with default values
var message = new gcm.Message();

// ... or some given values
var message = new gcm.Message({
	collapseKey: 'demo',
	priority: 'high',
	contentAvailable: true,
	delayWhileIdle: true,
	timeToLive: 3,
	restrictedPackageName: "somePackageName",
	dryRun: true,
	data: {
		key1: 'message1',
		key2: 'message2'
	},
	notification: {
		title: "Hello, World",
		icon: "ic_launcher",
		body: "This is a notification that will be displayed if your app is in the background."
	}
});

// Change the message data
// ... as key-value
message.addData('key1','message1');
message.addData('key2','message2');

// ... or as a data object (overwrites previous data object)
message.addData({
	key1: 'message1',
	key2: 'message2'
});

// Set up the sender with you API key
var sender = new gcm.Sender('insert Google Server API Key here');

// Add the registration tokens of the devices you want to send to
var registrationTokens = [];
registrationTokens.push('regToken1');
registrationTokens.push('regToken2');

// Send the message
// ... trying only once
sender.sendNoRetry(message, { registrationTokens: registrationTokens }, function(err, response) {
  if(err) console.error(err);
  else    console.log(response);
});

// ... or retrying
sender.send(message, { registrationTokens: registrationTokens }, function (err, response) {
  if(err) console.error(err);
  else    console.log(response);
});

// ... or retrying a specific number of times (10)
sender.send(message, { registrationTokens: registrationTokens }, 10, function (err, response) {
  if(err) console.error(err);
  else    console.log(response);
});

// Q: I need to remove all expired / unregistered tokens from my database, how do I do that?
//    The results-array does not contain any tokens!
// A: The array of tokens used for sending will match the array of results, so you can cross-check them.
sender.send(message, { registrationTokens: registrationTokens }, function (err, response) {
  var failed_tokens = registrationTokens.filter((token, i) => response.results[i].error === 'NotRegistered');
  console.log('These tokens are no longer registered:', failed_tokens);
});

var message = new gcm.Message();

// Add notification payload as key value
message.addNotification('title', 'Alert!!!');
message.addNotification('body', 'Abnormal data access');
message.addNotification('icon', 'ic_launcher');

// as object
message.addNotification({
  title: 'Alert!!!',
  body: 'Abnormal data access',
  icon: 'ic_launcher'
});

// Set custom request options
var requestOptions = {
	proxy: 'http://127.0.0.1:8888',
	timeout: 5000
};

// Set up the sender with your API key and request options
var sender = new gcm.Sender('YOUR_API_KEY_HERE', requestOptions);

// Prepare a GCM message...

// Send it to GCM endpoint with modified request options
sender.send(message, { registrationTokens: regTokens }, function (err, response) {
    if(err) console.error(err);
    else     console.log(response);
});