Updating state

Flat updates

Updating state with Zustand is simple! Call the provided set function with the new state, and it will be shallowly merged with the existing state in the store. Note See next section for nested state.

import { create } from 'zustand'

type State = {
  firstName: string
  lastName: string
}

type Action = {
  updateFirstName: (firstName: State['firstName']) => void
  updateLastName: (lastName: State['lastName']) => void
}

// Create your store, which includes both state and (optionally) actions
const usePersonStore = create<State & Action>((set) => ({
  firstName: '',
  lastName: '',
  updateFirstName: (firstName) => set(() => ({ firstName: firstName })),
  updateLastName: (lastName) => set(() => ({ lastName: lastName })),
}))

// In consuming app
function App() {
  // "select" the needed state and actions, in this case, the firstName value
  // and the action updateFirstName
  const firstName = usePersonStore((state) => state.firstName)
  const updateFirstName = usePersonStore((state) => state.updateFirstName)

  return (
    <main>
      <label>
        First name
        <input
          // Update the "firstName" state
          onChange={(e) => updateFirstName(e.currentTarget.value)}
          value={firstName}
        />
      </label>

      <p>
        Hello, <strong>{firstName}!</strong>
      </p>
    </main>
  )
}

Deeply nested object

If you have a deep state object like this:

type State = {
  deep: {
    nested: {
      obj: { count: number }
    }
  }
}

Updating nested state requires some effort to ensure the process is completed immutably.

Normal approach

Similar to React or Redux, the normal approach is to copy each level of the state object. This is done with the spread operator ..., and by manually merging that in with the new state values. Like so:

  normalInc: () =>
    set((state) => ({
      deep: {
        ...state.deep,
        nested: {
          ...state.deep.nested,
          obj: {
            ...state.deep.nested.obj,
            count: state.deep.nested.obj.count + 1
          }
        }
      }
    })),

This is very long! Let's explore some alternatives that will make your life easier.

With Immer

Many people use Immer to update nested values. Immer can be used anytime you need to update nested state such as in React, Redux and of course, Zustand!

You can use Immer to shorten your state updates for deeply nested object. Let's take a look at an example:

  immerInc: () =>
    set(produce((state: State) => { ++state.deep.nested.obj.count })),

What a reduction! Please take note of the gotchas listed here.

With optics-ts

There is another option with optics-ts:

  opticsInc: () =>
    set(O.modify(O.optic<State>().path("deep.nested.obj.count"))((c) => c + 1)),

Unlike Immer, optics-ts doesn't use proxies or mutation syntax.

With Ramda

You can also use Ramda:

  ramdaInc: () =>
    set(R.modifyPath(["deep", "nested", "obj", "count"], (c) => c + 1)),

Both ramda and optics-ts also work with types.

CodeSandbox Demo

https://codesandbox.io/s/zustand-normal-immer-optics-ramda-updating-ynn3o?file=/src/App.tsx

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