Does emit('my-event') emit to ALL clients or does the server know which client called .on('my-event')?

[MickL]

Lets say I have a complex website with multiple elements that I want to update by socket.io events. 10.000 clients are connected, but only 2 are currently at a specific side seeing a specific element and had called:

socket.on('my-event', (data) => { ... });

When the server now emits:

io.emit('my-event', { ... });

Does this event gets send to only the 2 that subscribed to the event, or does it get send to all 10.000 clients and the clients filter out what they are not interested in?

In any case, I think this is an important information that should be added to the docs, maybe here