Web3.js vs ethers.js in Blockchain / Solidity - Performance Comparison

Time Complexity: Web3.js vs ethers.js

O(n)

Understanding Time Complexity

When working with blockchain libraries like Web3.js and ethers.js, it's important to understand how their operations scale as you interact with the blockchain.

We want to see how the time to complete tasks grows when using these libraries with larger inputs or more complex calls.

Scenario Under Consideration

Analyze the time complexity of fetching multiple account balances using Web3.js and ethers.js.

// Using Web3.js
const balances = [];
for (let i = 0; i < accounts.length; i++) {
  const balance = await web3.eth.getBalance(accounts[i]);
  balances.push(balance);
}

// Using ethers.js
const balances = await Promise.all(
  accounts.map(account => provider.getBalance(account))
);
    

This code fetches the balance for each account from the blockchain using two different libraries.

Identify Repeating Operations

Look at what repeats as input grows.

• Primary operation: Fetching balance for each account.
• How many times: Once per account, so as many times as there are accounts.

How Execution Grows With Input

As the number of accounts increases, the number of balance fetches grows the same way.

Input Size (n)	Approx. Operations
10	10 balance fetches
100	100 balance fetches
1000	1000 balance fetches

Pattern observation: The work grows directly with the number of accounts.

Final Time Complexity

Time Complexity: O(n)

This means the time to get all balances grows in a straight line as you add more accounts.

Common Mistake

[X] Wrong: "Using Promise.all in ethers.js makes the operation constant time regardless of input size."

[OK] Correct: Even though Promise.all runs requests in parallel, each balance still needs to be fetched, so total work still grows with the number of accounts.

Interview Connect

Understanding how blockchain library calls scale helps you write efficient code and explain your choices clearly in conversations.

Self-Check

What if we batch multiple balance requests into a single call? How would the time complexity change?

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