How to Update an Object State Variable with useState

Updating a state variable that is defined as an object with properties can be a bit confusing when using the useState hook. Simply updating the object itself will not trigger a rerender of the component. However, there is a pattern that can be used to efficiently update the object state variable.

The pattern involves creating a temporary object with one property, and then using object destructuring to create a new object that combines the existing object with the temporary object.

Here’s an example of how to update an object state variable:

const [quizAnswers, setQuizAnswers] = useState({})

...

const updatedValue = {}
updatedValue[quizEntryIndex] = answerIndex
setQuizAnswers({
  ...quizAnswers,
  ...updatedValue
})

In this example, we create an empty object called updatedValue and add a property to it using square brackets notation. Then, we use object destructuring to create a new object that merges the existing quizAnswers object with the updatedValue object. This ensures that the state variable is updated correctly and triggers a rerender of the component.

Similarly, you can remove a property from the object state variable using the same pattern:

const copyOfObject = { ...quizAnswers }
delete copyOfObject['propertyToRemove']

setQuizAnswers({
  ...copyOfObject
})

In this case, we create a copy of the quizAnswers object using the spread operator and store it in the copyOfObject variable. Then, we remove the desired property using the delete keyword. Finally, we set the state variable quizAnswers to a new object that is a clone of copyOfObject, effectively removing the specified property.

By following this pattern, you can easily update and remove properties from an object state variable using the useState hook.

tags: [“React”, “useState”, “object state variable”, “updating state”, “useState with object”]