Custom Event on JavaScript Class

Question

How can I create an event that is attached to a class object?

I have to create a class that has an event that should be called at a certain time. The class looks like this and should call the event newMember when a new one is added. What works is that I attach a custom event to the window and call it which is not my goal.

Not NodeJS.

class Room {
    constructor() {
        this.members = {}
    }
    addMember(data) {
        if (!this.members[data.remotesid]) {
            this.members[data.socket] = data.identity
            //this.dispatchEvent();
        } else {
            console.log('Member already in room')
        }
    }
}