Recoil selector to capture the default values of atoms and merge them with arbitrary props.

recoilResetThenSetValue.js

import { atom, selector, selectorFamily, snapshot_UNSTABLE } from 'recoil'

const atomDefaults = {}

export const resetThenSetValue = selector ({
  key: 'resetThenSetValue',
  set: ({set}, {atom, ...rest}) => {
    set(atom,
      (prevValue) => {
        // Defaults not already stored
        if (!atomDefaults[atom.key]) {
          const isDefault = snapshot_UNSTABLE().getInfo_UNSTABLE(atom).isSet
          // Store incoming value as defaults.
          atomDefaults[atom.key] = isDefault ? {...prevValue} :
            // Backup in case atom was ininitally set by another method.
            Object.fromEntries(Object.entries(prevValue).map(
              _ => [_[0], _[1] instanceof Array ? [] : null]
            ))
          Object.freeze(atomDefaults[atom.key])
        }
        return {...atomDefaults[atom.key], ...rest}
      }
    )
  }
})