Use the subscribe API to add channels to the current list of subscribed channels. To unsubscribe from one or more of the currently subscribed channels, use the unsubscribe API and pass the channel(s) that need to be removed.

// subscribe to an initial array of channels
pubnub.subscribe({ channels: ['channel2', 'channel3'] });

// some time later in your code, you can add more channels to the existing list
pubnub.subscribe({ channels: ['channel4', 'channel5', 'channel10'] });

// at some point you may need to unsubscribe from some channels
pubnub.unsubscribe({ channels: ['channel3', 'channel2'] });

// finally, you can unsubscribe from all remaining channels

Here is the subscribe and unsubscribe JavaScript SDK docs.