为什么useState变量`const`在反应？

Question

My understanding is, when using useState() , we should declare the array as such:

const [someBooleanValue, setSomeBooleanValue] = useState(false)

Instead of

let [someBooleanValue, setSomeBooleanValue] = useState(false)

Normally, const is used on variables that won't be changing. Here, someBooleanValue will be changing. What is going on that allows us to use the const keyword in this case?

Answer 1

In React Hooks with a Functional Component, your code gets a single value of state for each call into your functional component. React handles the storage separately and returns that current value via useState on each execution of your code, providing the latest state value.

From the docs:

We declare a state variable called count, and set it to 0. React will remember its current value between re-renders, and provide the most recent one to our function. If we want to update the current count, we can call setCount.

So in this case, we use const because the value should never be reassigned in our code.

Answer 2

In the functional component, we declare the state using const. To update the state we have to go through a specific method that uses the Set function. It is completely fine to change the state by using the Set process.

We use const to avoid reassignment of state. That's shit!!!

Answer 3

const [someBooleanValue, setSomeBooleanValue] = useState(false)

is actually something like this

const handleState = useState(false)

handleState[0] is someBooleanValue and handleState[1] is setSomeBooleanValue .

This handleState is an array, which is a reference type. The handleState is just a pointer to that array and this pointer actually never changes.

someBooleanValue and setSomeBooleanValue are elements of the handleState array at index 0 and 1 .

So, someBooleanValue changes, not the pointer to the array in which it is contained.

Hope this clarifies!