how to use equivalent of flushSync ?

[arnaudambro]

Hello

I have a callback where I need to update an atom then use the new value of it.
It looks like

const [migrations, setMigrations] = useRecoilState(migrationsState)
const doMigrations = async () => {
  if (!migrations.includes('migration-1')) {
    // do some stuff
    setMigrations(m => [...m, 'migration-1'])
  }

  /* 
  NOW I NEED THE `migrations` to includes 'migration-1' before doing other stuff
  */

  console.log(migrations.includes('migration-1')) // false

  if (!migrations.includes('migration-2')) {
    // do some stuff
    setMigrations(m => [...m, 'migration-2'])
  }
}

in React, there is the flushSync that would do the thing, but I can't find out how to do achieve this in recoil

Is there a way ?

[drarmstr]

For atomic transactions you can use useRecoilTransaction_UNSTABLE(). The transaction will observe previous mutations. However, there are current limitations that only sync operations with atoms are supported. For more complete support you can use useRecoilCallback() which is provided a snapshot.
Snapshots are immutable, but you can transform it with map(), observe previous mutations as you go, and then goto the snapshot. If it is async, though, be careful of intervening operations.