Web3.js vs ethers.js in Blockchain / Solidity - Quick Revision & Key Differences

Recall & Review

beginner

What is Web3.js?

Web3.js is a JavaScript library that helps developers interact with the Ethereum blockchain by providing tools to send transactions, read blockchain data, and interact with smart contracts.

beginner

What is ethers.js?

Ethers.js is a lightweight JavaScript library designed to interact with the Ethereum blockchain. It focuses on simplicity, security, and providing a clean API for tasks like sending transactions and reading data.

intermediate

Name one key difference between Web3.js and ethers.js.

Web3.js is larger and older with more features, while ethers.js is smaller, more modular, and designed for better security and ease of use.

intermediate

Which library provides better support for ENS (Ethereum Name Service) resolution?

Ethers.js provides better and more straightforward support for ENS resolution compared to Web3.js.

intermediate

Why might a developer choose ethers.js over Web3.js?

A developer might choose ethers.js because it is easier to use, has better documentation, is more secure by design, and offers a smaller bundle size for web apps.

Which library is known for being more lightweight and modular?

A Neither is modular

B Web3.js

C ethers.js

D Both are equally heavy

Ethers.js is designed to be lightweight and modular, making it easier to use in modern web applications.

Which library was released first?

A Neither is related to Ethereum

B ethers.js

C Both released at the same time

D Web3.js

Web3.js is the older library and was released before ethers.js.

Which library offers better built-in support for ENS (Ethereum Name Service)?

A ethers.js

B Neither supports ENS

C Web3.js

D Both support ENS equally

Ethers.js provides better and more straightforward ENS support.

Which library is generally considered easier to learn for beginners?

A ethers.js

B Web3.js

C Both are equally difficult

D Neither is beginner-friendly

Ethers.js has a simpler API and better documentation, making it easier for beginners.

Which library is more focused on security by design?

A Web3.js

B ethers.js

C Both have the same security focus

D Neither focuses on security

Ethers.js emphasizes security and safer defaults in its design.

Explain the main differences between Web3.js and ethers.js.

Think about size, ease of use, and features.

Why might a developer prefer ethers.js for a new Ethereum project?

Consider developer experience and app performance.

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