Listen for new keys?

[frankier]

I'm interested in how to listen for new keys. It seems straightforward to listen for changes to an existing key if it's an observable, or listen for any change to the varhash or its children (I think - slightly hazy on how this works). But there doesn't seem to be any way to determine which/whether a key has been added or removed other than by diffing the whole hash with its previous value. Is this by design or would the addition of onaddition ondeletion methods which supply (key, value) and (key) to the callback respectively be reasonable?

[frankier]

Actually thinking about it, it is possible to hook into the creation function passed during construction. I guess diffing is more idiomatic?

[nrw]

The design of observ-* focuses around being able to ask very efficiently "is this the same as last time I checked?" observs are the same if they are ===.

I think adding add and delete events is outside of the scope of this project, but I'd be interested to hear thoughts from @Raynos about the matter.

[Raynos]

@nrw by design there should be an _diff field. ( https://github.com/nrw/observ-varhash/blob/master/index.js#L81 ).

When you listen to a change you can read the _diff field to get an efficient raw representation of what changed.

I've used this in the observ-array implementation to avoid implementing a naive diff of the full array each time anything changes.

[nrw]

@frankier does inspecting the _diff field on a change currently allow for the "listen for new keys" extension you seek?