Mostly I have seen in documentation and others code they wrote set hook like this picture in documentation:
in it they are changing count value by calling setCount. My question is that since count is declared with const keyword how is it changing on every setCount?
On re-renders, you are getting a new variable. setCount changes the value internally and ties the change into the life-cycle of the component. When a render occurs, you get a new count variable entirely, which is different than doing count = 9. Remember, components are just functions that are being called. Like any other function, each time you call it, you get a whole new set of variables scoped to it.
useState is returning an array with a value and a function, [9, () => {}]. All const [count, setCount] is doing is destructuring that array.
