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Awesome Open Source

Web3.js vs Ethers.js

A guide to the basic differences between Web3.js and Ethers.js, the two most popular libraries for interacting with the Ethereum blockchain. And two example frontend apps using React + Hooks!


Sample Dapp Contract

Inside the smart-contracts folder, you will find a simple Truffle project with the following Solidity contract:

pragma solidity ^0.5.0;

contract Counter {
  uint count = 0;

  function increment() public {
    count = count + 1;
  }

  function getCount() public view returns (uint) {
    return count;
  }
}

Setup Truffle project

Before you run any of the frontend UIs, make sure to start the development console with truffle develop, and then run the migrate command to compile and deploy the contract onto the development chain.

Two Frontend UIs

There are two folders (app-ethers and app-web3js) each containing a simple React frontend for the above contract. The only substantial difference between these two UIs is located in the useCounterContract.js files.

Here are the direct links for your convenience:

Running the apps

In each of these apps, you can serve the frontends with the following commands:

npm install
npm start

This will serve the frontend on http://localhost:1234 which you can view in your browser.

Differences

There are three major portions in this code: the setup, reading (calling a constant method), and writing (calling a non-constant mutating method).

Setup

With Web3.js, we need the following to instantiate a connected contract instance that can make read/write calls:

  • contract ABI
  • deployed contract address
  • a from address (for send transactions)

Note that the networkId is required for us to fetch the deployed address from our contract artifact.

// Web3.js
const web3 = new Web3("http://127.0.0.1:8545");
const accounts = await web3.eth.getAccounts();
const networkId = await web3.eth.net.getId();
const contractAddress = artifact.networks[networkId].address;

contractInstance = new web3.eth.Contract(artifact.abi, contractAddress, {
  from: accounts[0],
});

With Ethers.js, we need the following for our contract instance:

  • deployed contract address
  • contract ABI
  • a Signer object (similar to Provider, but with a specified Signer)
// Ethers.js
const provider = new ethers.providers.JsonRpcProvider();
const network = await provider.getNetwork();
const contractAddress = artifact.networks[network.chainId].address;

contractInstance = new ethers.Contract(
  contractAddress,
  artifact.abi,
  provider.getSigner(),
);

Calling a constant method

// Web3.js
const count = await contractInstance.methods.getCount().call();
console.log(count); // returns a String
// Ethers.js
const count = await contractInstance.getCount();
console.log(count); // returns a BigNumber instance

These two are very similar, but in our example Ethers.js returns a BigNumber instance by default whereas Web3.js will return the number as a String.

Calling a non-constant method

// Web3.js
await contract.current.methods.increment().send();
// tx has been mined
// Ethers.js
const tx = await contract.current.increment();
await tx.wait(); // wait for mining

Note that Web3.js will return a PromiEvent which allows you to subscribe to confirmations, errors, and the transaction hash.

Ethers.js will return a transaction object where a bunch of information relating to the transaction is kept. You can grab the hash via tx.hash, but you must await on tx.wait() if you want to make sure it has been mined.


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