useMemo hook in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the useMemo hook from React.

React

import React, { [1] } from 'react';

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

AuseMemo

BuseState

CuseEffect

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing useMemo with useState or useEffect.

The useMemo hook is imported from React to memoize expensive calculations.

2fill in blank

medium

Complete the code to memoize the result of the expensiveFunction using useMemo.

React

const memoizedValue = useMemo(() => expensiveFunction(), [1]);

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A[memoizedValue]

B[expensiveFunction]

C[value]

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using the function itself as a dependency causing repeated calls.

Passing an empty array [] means the function runs only once on mount.

3fill in blank

hard

Fix the error in the useMemo usage to correctly memoize based on 'count'.

React

const memoizedValue = useMemo(() => computeValue(count), [1]);

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A[]

Bcount

C[count]

D[computeValue]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a single variable instead of an array as dependency.

The dependency array must be an array containing count to update memoizedValue when count changes.

4fill in blank

hard

Fill both blanks to memoize the sum of a and b, updating only when a or b changes.

React

const sum = useMemo(() => [1] + [2], [a, b]);

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Aa

Bb

Csum

DuseMemo

Attempts:

3 left

💡 Hint

Common Mistakes

Using the memoized variable inside its own calculation.

The sum is calculated by adding a and b inside useMemo.

5fill in blank

hard

Fill all three blanks to create a memoized object with keys 'x', 'y', and 'z' from props.

React

const memoizedObj = useMemo(() => ({ x: [1], y: [2], z: [3] }), [props.x, props.y, props.z]);

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

Aprops.x

Bprops.y

Cprops.z

DmemoizedObj

Attempts:

3 left

💡 Hint

Common Mistakes

Using the memoized object inside its own definition.

The object keys get their values from props.x, props.y, and props.z respectively.