there should be tests with multiple concurrent Events to prevent passing the state with global variables

the it block should have no other public properties will contain no assertions when Event has no enumerable properties at all, causing the assertion to be displayed in Red even though it passes

Read this for more info

OP solved it, closing

You have an error in unsubscribe method, it does not remove the corresponding functions correctly because you are missing one argument to a particular function which by default will be 0.

OP solved it, closing

OP left the building

OP solved it, closing

Ranks on old katas can't be changed

Ranks on old katas can't be changed

No tests, description not sufficient for solutions

any hints?

should be upgraded to modern JS/Node, with a class in the initial code

python fork with new test framework

Handlers (handling functions) are the subscribers of your Event object. The invocation context of a function is a value you get when you reference this inside the function. The requirement is, this inside the handlers should point to this of the emit method, i.e. the instance of the Event object. The error tells you it's not happening in your case.

This functionality is needed so you could subscribe and unsubscribe to the event from within your handlers, like this:

const myEvent = new Event();

myEvent.subscribe(() => {
  // notice the use of "this" instead of the explicit "myEvent"
  this.subscribe(/* ... */);
  this.unsubscribe(/* ... */);
})