Web3.js vs ethers.js in Blockchain / Solidity - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new instance of Web3 using a provider.

Blockchain / Solidity

const Web3 = require('web3');
const web3 = new Web3([1]);

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

Awindow.ethereum

Bethers.providers.JsonRpcProvider

Cnew ethers.providers.Web3Provider()

Dweb3.eth

Attempts:

3 left

💡 Hint

Common Mistakes

Using ethers.js provider instead of Web3.js provider.

In Web3.js, you create a new instance by passing a provider like window.ethereum.

2fill in blank

medium

Complete the code to create a new ethers.js provider connected to a JSON RPC URL.

Blockchain / Solidity

const { ethers } = require('ethers');
const provider = new ethers.providers.[1]('https://mainnet.infura.io/v3/YOUR-PROJECT-ID');

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

AWeb3Provider

BAlchemyProvider

CJsonRpcProvider

DInfuraProvider

Attempts:

3 left

💡 Hint

Common Mistakes

Using Web3Provider which expects a web3 provider object.

Use JsonRpcProvider to connect to a JSON RPC URL in ethers.js.

3fill in blank

hard

Fix the error in the code to get the balance of an address using ethers.js.

Blockchain / Solidity

const balance = await provider.getBalance([1]);

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

A12345

B'0x742d35Cc6634C0532925a3b844Bc454e4438f44e'

Cprovider.address

Dethers.utils.getAddress()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a number or invalid object instead of a string address.

The getBalance method requires a valid Ethereum address as a string.

4fill in blank

hard

Fill both blanks to create a contract instance using ethers.js with ABI and address.

Blockchain / Solidity

const contract = new ethers.Contract([1], [2], provider);

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

A'0x1234567890abcdef1234567890abcdef12345678'

Babi

Caddress

Dprovider

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping address and ABI positions.

The first argument is the contract address as a string, the second is the ABI array.

5fill in blank

hard

Fill all three blanks to send a transaction using Web3.js with from address, to address, and value.

Blockchain / Solidity

web3.eth.sendTransaction({ from: [1], to: [2], value: [3] });

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

A'0xYourAddressHere'

B'0xRecipientAddressHere'

C'1000000000000000000'

D'someValue'

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers instead of strings for addresses or value.

Use string addresses for from and to, and a string of wei for value.

Practice

1. Which of the following is a key difference between Web3.js and ethers.js?

easy

A. ethers.js is a backend-only library, Web3.js is frontend-only.

B. Web3.js only works with Bitcoin, ethers.js only with Ethereum.

C. ethers.js cannot send transactions, Web3.js can.

D. Web3.js is larger and older, while ethers.js is lighter and simpler.

Solution

1. Step 1: Understand library origins

   Web3.js is an older, larger library designed for Ethereum interaction.

2. Step 2: Compare library features

   ethers.js is newer, designed to be lightweight and simpler to use.

3. Final Answer:

   Web3.js is larger and older, while ethers.js is lighter and simpler. -> Option D

4. Quick Check:

   Library size and age = A [OK]

Hint: Remember: Web3.js is big and old; ethers.js is small and new [OK]

Common Mistakes:

• Thinking ethers.js only works on backend
• Confusing blockchain support (Bitcoin vs Ethereum)
• Believing ethers.js can't send transactions

2. Which of the following is the correct way to create a provider using ethers.js?

easy

A. const provider = new ethers.providers.JsonRpcProvider();

B. const provider = new Web3.providers.HttpProvider();

C. const provider = new ethers.Web3Provider();

D. const provider = new Web3.eth.JsonRpcProvider();

Solution

1. Step 1: Recall ethers.js provider syntax

   ethers.js uses ethers.providers.JsonRpcProvider() to create a JSON RPC provider.

2. Step 2: Identify correct syntax

   const provider = new ethers.providers.JsonRpcProvider(); matches the correct ethers.js syntax; others mix Web3.js or incorrect classes.

3. Final Answer:

   const provider = new ethers.providers.JsonRpcProvider(); -> Option A

4. Quick Check:

   ethers.js provider creation = D [OK]

Hint: ethers.js uses ethers.providers.JsonRpcProvider() [OK]

Common Mistakes:

• Mixing Web3.js and ethers.js syntax
• Using Web3 classes with ethers.js
• Incorrect capitalization or namespaces

3. What will be the output of this ethers.js code snippet?

const ethers = require('ethers');
const provider = new ethers.providers.JsonRpcProvider();
(async () => {
  const blockNumber = await provider.getBlockNumber();
  console.log(blockNumber);
})();

medium

A. An error because getBlockNumber() is not a function.

B. Undefined because provider is not initialized.

C. The current Ethereum block number as a number.

D. A string 'blockNumber' printed to console.

Solution

1. Step 1: Understand provider and method

   The JsonRpcProvider connects to Ethereum and getBlockNumber() returns the latest block number as a number.

2. Step 2: Analyze async function output

   The code logs the block number to console, so output is a number representing current block.

3. Final Answer:

   The current Ethereum block number as a number. -> Option C

4. Quick Check:

   getBlockNumber() returns number [OK]

Hint: getBlockNumber() returns a number, not error or string [OK]

Common Mistakes:

• Expecting a string instead of number
• Thinking getBlockNumber() is missing
• Assuming provider is uninitialized

4. Identify the error in this Web3.js code snippet:

const Web3 = require('web3');
const web3 = new Web3();
(async () => {
  const balance = await web3.eth.getBalance('0x123...');
  console.log(balance);
})();

medium

A. Missing provider URL when creating Web3 instance.

B. getBalance() is not an async function.

C. The address format is incorrect.

D. console.log cannot print balance.

Solution

1. Step 1: Check Web3 instance creation

   Web3 requires a provider URL (like HTTP or WebSocket) when instantiated to connect to Ethereum.

2. Step 2: Identify missing provider

   The code creates new Web3() without a provider, so calls like getBalance will fail.

3. Final Answer:

   Missing provider URL when creating Web3 instance. -> Option A

4. Quick Check:

   Web3 needs provider URL [OK]

Hint: Always pass provider URL to Web3 constructor [OK]

Common Mistakes:

• Thinking getBalance is not async
• Assuming address format is wrong
• Believing console.log can't print balance

5. You want to send a transaction using ethers.js and wait for it to be mined. Which code snippet correctly does this?

hard

A. const tx = await provider.sendTransaction(txData);
await tx.wait();

B. const tx = await signer.sendTransaction(txData);
await tx.wait();
console.log('Mined:', tx.hash);

C. const tx = signer.sendTransaction(txData);
console.log('Mined:', tx.hash);

D. const tx = await signer.send(txData);
await tx.wait();

Solution

1. Step 1: Identify correct method to send transaction

   In ethers.js, signer.sendTransaction() sends a transaction and returns a transaction response.

2. Step 2: Wait for transaction mining

   Calling tx.wait() waits for the transaction to be mined before proceeding.

3. Step 3: Confirm correct usage

   const tx = await signer.sendTransaction(txData; await tx.wait(); console.log('Mined:', tx.hash); correctly awaits sending, then waits for mining, then logs the hash.

4. Final Answer:

   const tx = await signer.sendTransaction(txData); await tx.wait(); console.log('Mined:', tx.hash); -> Option B

5. Quick Check:

   sendTransaction + wait() = C [OK]

Hint: Use sendTransaction() then wait() to confirm mining [OK]

Common Mistakes:

• Not awaiting sendTransaction()
• Using provider instead of signer to send
• Calling non-existent send() method