Class based react

Question 1

What does super() do in a class based component?

Answer 1

it calls the parents classes constructor. So when you extend from React.Component it calls using super() calls React.Component’s constructor function.

Question 2

When does componentDidMount run?

Answer 2

Immediately after the first render of a component.

Question 3

What triggers a component to run the render method again?

Answer 3

Whenever props or state change a component will re render.

Question 4

What is the equivalent to componentDidMount when working in a functional component?

Answer 4

a useEffect with an empty dependency array.

Question 5

When does componentDidUpdate run?

Answer 5

If you define the componentDidUpdate method, React will call it immediately after your component has been re-rendered with updated props or state. This method is not called for the initial render.

Question 6

When does the componentWillUnmount run? What is it useful for?

Answer 6

If you define the componentWillUnmount method, React will call it before your component is removed (unmounted) from the screen. This is a common place to cancel data fetching or remove subscriptions.

Question 7

What does a Redux Provider do? How does it do this?

Answer 7

The <Provider> component makes the Redux store available to any nested components that need to access the Redux store.</Provider>

It uses React’s Context mechanism to do this.

Question 8

What does React context let you do ?

Answer 8

Context lets components pass information deep down without explicitly passing props.