Is the 'on' method in this node.js code a JavaScript method or a node method?

I couldn't find this answer on Google because 'on' is such a common word. In this node.js example:

conn.on('close', function() {
var pos =   connections.indexOf(conn);
    if (pos >= 0) {
        connections.splice(pos, 1);
    }
});

There is a .on method(?). What it does? It is a JavaScript method? Or it is something you only find in node? I'm kind of confused because I think I saw something like .on on jQuery. Is it similar to the jQuery .live event handler?

Can anyone explain this to me?

It is a method from Node's EventEmitter class:

https://nodejs.org/docs/latest/api/events.html#events_emitter_on_eventname_listener

In this case, on is a node method. jQuery also has a method of the same name, and they're used for basically the same purpose - binding event handlers to events by their string name. In fact the signatures look identical to me, IIRC.

Pure JavaScript doesn't have such a method.