React Hooks useState Hook

Question 1

What does the useState hook return?

Accepted Answer

An array with a state value and a setter function

Answer

useState returns a tuple of [currentValue, setterFunction] that you destructure.

Question 2

What is the initial value passed to useState used for?

Accepted Answer

It sets the state only on the first render

Answer

The initial value is only used during the first render; subsequent renders use the current state.

Question 3

Which of the following correctly initializes a counter state to 0?

Accepted Answer

const [count, setCount] = useState(0)

Answer

Array destructuring with both the state variable and its setter is the correct pattern.

Question 4

What happens if you call the setter function returned by useState with the same value as the current state?

Accepted Answer

React bails out of the re-render

Answer

React uses Object.is comparison; if the value hasn't changed, it bails out of re-rendering.

Question 5

How do you update state based on the previous state value?

Accepted Answer

setCount(prev => prev + 1)

Answer

Using a functional update (prev => prev + 1) ensures you always operate on the most recent state.

React Practice Test