React setState() update nested object

DanielApril 19, 2023April 20, 2023

There are two sides to the story of updating nested state objects in React.

The short answer

The easiest way to update a nested object stored in the React state is to create a shallow copy and use the spread operator.

Updating a 1-level deep object

Let's say we have the below object in a React state variable:

const [cat, setCat] = useState({
    name:'Achilles the 😸',
    origin: 'Greece 🇬🇷',
    owner: {
        name: "Daniel", 
        age: 38
    }
})

To update a 1-level deep property, eq owner.name, we can do:

setCat(prevCat => ({
    ...prevCat,
    owner: {
        ...prevCat.owner,
        name: "Daniel the owner of Achilles"
    }
}))

Updating a 2-levels deep object

If we have a more complex nested object, like the one below:

const [cat, setCat] = useState({
    name:'Achilles the 😸',
    origin: 'Greece 🇬🇷',
    owner: {
        name: "Daniel", 
        age: 38,
        job: {
            title: "Software Developer", 
            location: "At home"
        }
    }
})

We can use the same approach, but the mind the extra deep of the state object:

setCat(prevCat => ({
    ...prevCat,
    owner: {
        ...prevCat.owner,
        job : {
            ...prevCat.owner.job,
            title: 'Cat slave'
        }
    }
}))

I've made this example on Github. And you can see it live here.

For 3 nesting levels and above keep in mind to spread each level of the nested object.

The long answer

The long answer is ... don't use setState() to update nested objects!

The nested state is a wrong design pattern, given that React embraces the concept of state immutability.

We can try to flatten the state. For example:

// before 
const [cat, setCat] = useState({
    name:'Achilles the 😸',
    owner: {
        name: "Daniel", 
    }
})

// after 
const [cat, setCat] = useState({
    name:'Achilles the 😸',
    ownerName: "Daniel"
})

You can flatten your state by hand or use a third-party library similar to Normalirz.

Another solution is to use immutable helpers such as immutability-helper or immer.