The Subscribe Button has been updated so that users do not subscribe to or unsubscribe from a channel just by clicking on a button. Now, when a user clicks on a button, the channel page associated with that button opens in a new window.
If the user was not previously subscribed to the channel, the page displays a confirmation dialog so that the user can verify the intent to subscribe to the channel.
If the user was already subscribed to the channel, the user can unsubscribe from the channel page.
The Subscribe Button no longer fires an event when a user clicks the button to subscribe to or unsubscribe from a channel. (The button had supported subscribe and unsubscribe events.) The data-ytonevent attribute, which could previously be used to specify an event listener, has also been deprecated.
In light of this change, the gapi.ytsubscribe.render method no longer supports the onytevent option, which could previously be used to specify an event listener