var FCM = require('fcm-node');
var serverKey = 'SERVER-KEY-COMES-HERE'; //put your server key here
var fcm = new FCM(serverKey);

var message = {
   "to":'FCM-TOKEN-COMES-HERE',
   "content_available": true,
   "mutable_content": true,
    "notification": {
        "title": 'title comes here',
        "body": 'body comes here',
        "sound": "default",
    },
    "data": {
        "title": 'title comes here',
        "body": 'body comes here',
        "custom_var": 'yes'
    }
};

fcm.send(message, function (err, response) {
    if (err) {
        console.log('error);
    } else {
        console.log("Successfully sent with response: ", response);
    }
});