JavaScript KeyboardEventInit.which

According to MDN, the KeyboardEventInit dictionary which is used to pass values to a new instance of KeyboardEvent through its constructor new KeyboardEvent(init) includes the which field as one of the allowed initialization values.

KeyboardEvent on MDN

However, in testing with the following piece of JavaScript code, it becomes clear that this does not actually set the which keyboard event property value:

new KeyboardEvent({ which: 190 }).which

This expression always evaluates to 0 which is the default for which if not provided, so the code behaves as if which is not provided in the initialization dictionary.

Is it perhaps because which must be provided in conjunction with some other field of the same dictionary?

The Conclusion

LOL, turns out, yeah, there are implicit dependencies between the various fields of the init dictionary as evidenced by the fact that when serializing all the enumerable fields of an existing keyboard event and then initializing a new event off that dictionary, the resulting even has a working which.

This makes sense, actually, it should be impossible to construct an event whose key says it is an Enter key but whose code or which say something different. But the JS API is, as is almost customary in the broader JS browser API ecosystem, absolute garbage. It could stand a more type-safe treatment, or at least should throw better (any!) errors, but it is too late for that by now. :-)