common: re-write `map() ` to work like Array.map

[josephjclark]

common currently has a function called map, which so far as I can tell is exactly the same as each (but is documented wrongly).

I think map should work like Javascript's native Array.map.

Given an array, it will iterate over each item and call a function. The returned value is added to a new array. Once iteration is complete, the new array is written to state.

Unlike each, it does not take an operation as a callback function. Just a function. That's because the return value is not treated like state.

Like each, it should pass a scoped state object, where data is the item under iteration and the rest of your state is normal.

At the end, map should return the new state object, just like any other operation.

It could take options:

• if filter is true, returning null will remove the item from the array. Default true.
• if statePath is set, the new array will be written to this path on state

That leaves us with a signature like

map(path, callback, options)

it's pretty weird too have options after callback, but also weird to force options.

[josephjclark]

I guess one question on this one is: should we actually RESERVE the word map? Does the implementation team use map in the same way as we do? I think so but I just wonder if there's a semantic gap there

[mtuchi]

After having a chat with @josephjclark this issue seems to be unimportant and needs more clarity on what's need to be implemented if we think people are going to use this helper function.

@aleksa-krolls I suggest we put a pause until @josephjclark is back online

[aleksa-krolls]

Noted @mtuchi pls move to Blocked for this week, and we can revisit this at a later date once we hear from @josephjclark