Subscription prop about constate

[billykwok]

Is the shouldUpdate prop in Container good enough for this use case? Other than than being a syntax shortcut, what benefits would it bring? I just personally think that shouldUpdate is clearer and short enough.

[diegohaz]

I guess the first case using shouldUpdate would look like this:

<Container
  initialState={{ foo: "foo", bar: "bar" }}
  shouldUpdate={({ state, nextState }) => state.foo !== nextState.foo}
/>

But it can get more complex:

// subscribe to "a", "b" and "c.b"
<Container
  initialState={{ a: "a", b: "b", c: { a: "a", b: "b" }, d: "d" }}
  shouldUpdate={({ state, nextState }) => (
    state.a !== nextState.a ||
    state.b !== nextState.b ||
    state.c.b !== nextState.c.b
  )}
/>

// or
<Container
  initialState={{ a: "a", b: "b", c: { a: "a", b: "b" }, d: "d" }}
  shouldUpdate={({ state, nextState }) => (
    state.c.a === nextState.c.a &&
    state.d === nextState.d
  )}
/>

The case above with subscription:

// subscribe to "a", "b" and "c.b"
<Container
  initialState={{ a: "a", b: "b", c: { a: "a", b: "b" }, d: "d" }}
  subscription={{ a: true, b: true, "c.b": true }}
/>

// or
<Container
  initialState={{ a: "a", b: "b", c: { a: "a", b: "b" }, d: "d" }}
  subscription={{ "c.a": false, d: false }}
/>

The problem with shouldUpdate is that it can be hard to read and reason about. At the same time, we need to keep it as a low level API.

But, in the end, it depends on how often people would need something as subscription. For pure, for example, I was using it almost everywhere (I even considered making it true by default, but it could have some silent unintended side effects), so it was worth creating a prop for it.

The only situation I really wanted this subscription was when I was building a complex Form Container.