Allow a custom merge method

Currently, when a action return a new state, this one is merged with the previous state. That make the object “state” to grow but never shrink. I would imagine this behavior to be configurable with a pure function. where the default would be:

const mergeState = (previousState, newState) => ({...previousState, ...newState});

To have the same behavior as redux for example, we can use this function

const mergeState = (previousState, newState) => newState;

[whaaaley]

I like the idea of non-merged state. I know merged state has it’s own pros, but merging doesn’t really help me with my own apps.

If I have some state like this and and I want to update the state.

// initial
{
  foo: 'bar',
  bar: 'baz'
}

// now i want this
{
  foo: 'ooga booga'
}

I won’t be able to. I’d have to set bar to null myself to denote that it’s “removed”.

// initial
{
  foo: 'bar',
  bar: 'baz'
}

// now i want this
{
  foo: 'ooga booga',
  bar: null
}

And of course, as your state gets more complex, it’s not as easy as setting a single prop to null.

It’s not a “con” per se. It’s just a way I would prefer to build my apps. Imo, when being able to replace a state object “wholesale” like this, it’s easier to read and less code to write, both with actions and in views.

Right now a way around this is to just put everything one level deeper to avoid the merge.

When state wasn’t immutable, I’d imagine leaving “removed” state as null would be a perf gain, as you wouldn’t need to constantly, remove and re-create that prop, but now that everything is immutable, there’s not anything to gain, perf wise.

[jorgebucaran]

I don’t consider this to be remotely critical, but I would reconsider if it was. However, none of the answers has been able to justify adding this, so I am gonna go with @okwolf’s and avoid us option paralysis.

This is by far the most common use case, and the only one I’ve used in reducers for Redux.

EDIT: If this turns out to be relevant to implementing something important in the future, I am happy to reopen and add it.