linkChange Verification

Sometimes you might want to verify changes before they are broadcast. The verified() method (and the VerifiedState class) facilitates such verifications by only accepting changes from sub-states that are verified by given verification function.

For example, imagine you want a state whose value can only increase:

1linkimport { state, verified } from 'rxdeep';

2link

3linkconst ascending = verified(state(3), 

4link  change => !!change.value                         // --> not changing to `undefined

5link  && change.trace.from < change.trace.to           // --> we are changing to a larger value

6link)

7link

8linkascending.subscribe(console.log);

9link

10linkascending.value = 2;             // --> rejected

11linkascending.value = 4;             // --> accepted

12linkascending.value = 7;             // --> accepted

13linkascending.value = 5;             // --> rejected

14link

15link// Logs:

16link// > 3

17link// > 3 --> for the rejected 2

18link// > 4

19link// > 7

20link// > 7 --> for the rejected 5

info NOTE

You can also utilize VerifiedState class constructor instead of verified() function.

Each VerifiedState (created with verified()) is a child of State with all the same methods and attributes. The only difference is that it executeds the given verification method on each incoming change, and if the change is rejected, it will not send it upstream, but instead reverse the change and broadcast the reverse downstream so that sub-states correct their corresponding values.