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    Compute a Value in Recoil Using a Selector

    reactReact

    To compute a value from one or more values stored in Recoil, we can create a "selector".

    First import selector from Recoil, and then call it with an object that has two keys: key and get:

    import { selector } from recoil;
    ...
    const paperSize = selector({
      key: 'paperSize',
      get: ({get}) => {
        const score = get(gameScore)
        return 100 + (score * 5)
      }
    })

    Inside of the get function we can get the current value of the gameScore atom from recoil, and then compute a new value from that to return to our game. Then we can get the value using useRecoilValue:

    import { paperSize } from './selectors'
    ...
    const size = useRecoilValue(paperSize)