Avoiding unnecessary renders in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a state variable using React hooks.

React

const [count, [1]] = useState(0);

Drag options to blanks, or click blank then click option'

AcountSet

BupdateCount

CsetCount

DchangeCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using a name that does not start with 'set' for the update function.

Swapping the order of the state and update function.

The useState hook returns a pair: the current state and a function to update it. The convention is to name the update function as set plus the state variable name.

2fill in blank

medium

Complete the code to memoize a value and avoid recalculating it on every render.

React

const doubled = useMemo(() => count * 2, [[1]]);

Drag options to blanks, or click blank then click option'

Acount

Bdoubled

CsetCount

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving the dependency array empty, causing stale values.

Including the memoized variable itself, causing infinite loops.

The dependency array tells React when to recalculate the memoized value. It should include the variables that affect the calculation, here count.

3fill in blank

hard

Fix the error in the code to prevent unnecessary re-renders by wrapping the callback with the correct hook.

React

const increment = [1](() => setCount(count + 1), [count]);

Drag options to blanks, or click blank then click option'

AuseCallback

BuseState

CuseMemo

DuseEffect

Attempts:

3 left

💡 Hint

Common Mistakes

Using useEffect instead of useCallback.

Not wrapping the function at all, causing new function instances each render.

useCallback returns a memoized version of the callback that only changes if its dependencies change. This helps avoid unnecessary re-renders when passing callbacks to child components.

4fill in blank

hard

Fill both blanks to create a memoized component that only re-renders when its props change.

React

const MemoizedButton = [1](Button);

export default [2];

Drag options to blanks, or click blank then click option'

Amemo

BButton

CMemoizedButton

DuseMemo

Attempts:

3 left

💡 Hint

Common Mistakes

Exporting the original component instead of the memoized one.

Using useMemo instead of memo for components.

memo is a higher-order component that memoizes the wrapped component. The exported component should be the memoized one to avoid unnecessary renders.

5fill in blank

hard

Fill all three blanks to optimize a list rendering by memoizing the item renderer and using keys correctly.

React

const renderItem = [1]((item) => {
  return <li key={item.[2]>{item.[3]</li>;
}, [items]);

Drag options to blanks, or click blank then click option'

AuseCallback

Bid

Cname

DuseMemo

Attempts:

3 left

💡 Hint

Common Mistakes

Using useMemo instead of useCallback for functions.

Using non-unique values for keys causing rendering issues.

useCallback memoizes the function to avoid recreating it each render. The key prop should be a unique identifier like id. The displayed content is the name property.