为什么React UseState返回const数组

Question

I am currently learning React and React hook. A classic example of using useState is as below:

const [count, setCount] = useState(0);

My question is why the returned array is const? I think at least the value of count is changed over time.

Answer 1

The value returned by useState is not a const array, rather its just an array which the user has decided to declare as const . Think of the above as

const stateValue = useState(0);
const count = stateValue[0];
const setCount = stateValue[1];

So in short, the syntax const [count, setCount] = useState(0); is an Array destructuring syntax .

Not its is declared as const because you are not reassigning count or setCount to something else in your code, instead just using setCount method to update the state count.

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React authors decided to return an array with state value and state setter so that you can name it anything you want instead of using a pre-decided name while destructuring.