FCM provides a platform that helps you send the messages and notifications to the app user in real-time using service workers. You can send hundreds of billions of messages per day for free across different platforms: Android, iOS, and web (Javascript). You can also schedule the message delivery, immediately or in future.

There are two main components in  FCM implementation: a trusted environment that includes an app server or a Cloud function to send the messages, and an iOS, Android, or web (JavaScript) client app that receives the messages.

If you know about the Google Cloud Messaging (GCM), you might have a question of how FCM is different from GCM. The answer to this question is that FCM is the latest and improved version of GCM. It inherits all the infrastructure of GCM and carries improvements for the simplified client development. Just note that GCM is not deprecated and Google is still supporting it. However, the new client-side features will only come to FCM and hence as per Google recommendation, you should upgrade from GCM to FCM.

Though it supports different platforms, Android, iOS, and Web, we will mainly talk about web (Javascript) in this chapter. Let's now look at the key features of FCM.