subscribe( )

Subscribes to a channel or channel resource.

The subscribe() function subscribes to receive messages published on the specified channel or channel resource and sets a function that handles incoming messages when they are published to the channel.

When you subscribe to a channel you do not receive messages published to a resource on that same channel. To receive those messages, you must explicitly subscribe to the specific resource.

The specified message handler is run each time a message is published on the given channel or channel resource. Use it to define what happens when messages are received.

You can subscribe to a channel or channel resource more than once to add multiple message handlers. Each subscription returns a unique subscription ID which can be used later to unsubscribe from the specific subscription with that ID, without affecting the other subscriptions on the same channel or channel resource.