The proposal used to do more thing and we didn't change the URL after we ultimately arrived at this set of APIs.

> Their usage of upsert appears different than I was used to: > Them: Upsert = Get or Insert

I agree that their choice of labeling the proposal as "upsert" is less than ideal. However, this functionality is reminiscent of a very useful Perl capability known as autovivification[0] as described in the motivation section:

  A common problem when using a Map or WeakMap is how to 
  handle doing an update when you're not sure if the key 
  already exists in the map.

0 - https://en.wikipedia.org/wiki/Autovivification

Reminds me of the weird C++ map operator[] behavior.

If you use that operator and the value doesn't exist, it'll default create one and return a reference to that.

And as I'm writing this I realize why... references cannot be `null`.

what is the value of an "update or insert" call on `Map`? is that not just set?

`getOrInsert` here seems to be the Python "set_default" method on dicts, which is very useful at avoiding tedium in some basic data munging

I do this all the time, getOrInsert would come really handy: you need something from a Map-backed storage, but the value may be unset, so you first check if it's undefined, set the default value, and then use that.

Example:

    update(store, (draft) => {
      if (!draft.alertConfigurations.has(req.params.clusterId))
        draft.alertConfigurations.set(req.params.clusterId, new Map());
      const clusterAlerts = draft.alertConfigurations.get(req.params.clusterId);
      req.body.forEach((alert) => clusterAlerts.set(alert.id, { ...alert, predefined: false }));
    });

> what is the value of an "update or insert" call on `Map`?

It gives a caller the option of alternate logic based on the existence, or lack thereof, of a value.

> is that not just set?

No. The semantics of a "set" operation would overwrite an existing entry (if one exists).