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Posted on • Updated on • Originally published at blog.hdks.org

Ethers.js Cheat Sheet

#ethers #web3 #javascript

ethers.js is a library that interact with Ethereum Blockchain.

It is a very useful library but the official documentation was a little hard to read for me so I would like to summarize it for easy reference. (Focusing on what will be used often.)

*They are arranged in alphabetical order.

Accounts

Gets a list of accounts

const accounts = await provider.listAccounts();
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Example:

// Connect web3
const provider = new ethers.providers.Web3Provider(window.ethereum);

const accounts = await provider.listAccounts();
console.log(accounts[0]);
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Balance

Gets a blanace of address

const balance = await provider.getBalance(`address`);
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Example:

// Connect web3
const provider = new ethers.providers.Web3Provider(window.ethereum);

const address = "0x28d3...";

const balance = await provider.getBalance(address);

console.log(`The ${address} balance: ${balance.toString()}`);
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Connect (MetaMask)

Connects to Ethereum with MetaMask

const provider = new ethers.provider.Web3Provider(window.ethereum);
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Connect (RPC)

Connects to Ethereum with RPC

const provider = new ethers.provider.JsonRpcProvider(`url`);
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url for example:

Platform URL
Alchemy https://<network>.alchemyapi.io/v2/YOUR-API-KEY
Infura https://<network>.infura.io/v3/YOUR-PROJECT-ID

Contract

Create a contract instance by signer.

It does not work if the user does not have a wallet or is not connected.

const contract = new ethers.Contract(`address`, `abi`, `signer`);
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Example:

import Artifact from './Contract.json';

// Connect web3
const provider = new ethers.providers.Web3Provider(window.ethereum);
const signer = provider.getSigner();

const contractAddress = "0x9fE4...";

const contract = new ethers.Contract(
    contractAddress,
    Artifact.abi,
    signer
);

// Call a state-change method
const userAddress = "0x28d3...";
const dai = ethers.utils.parseUnits("1.0", 18);
await contract.transfer(userAddress, dai);
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Contract (Read-Only)

Create a contract instance by provider.

It can call Read-Only methods only. Instead, it also works if the user doesn't have a wallet or isn't connected.

const contract = new ethers.Contract(`address`, `abi`, `provider`);
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Example:

import Artifact from './Contract.json';

// For example here, interact with Alchemy JSON-RPC
const provider = new ethers.providers.JsonRpcProvider("https://eth-mainnet.alchemyapi.io/v2/<YOUR-API-KEY>");

const contractAddress = "0x9fE4...";

const contract = new ethers.Contract(
    contractAddress,
    Artifact.abi,
    provider
);

// Call a getter method
const contractName = await contract.name();
console.log(`Contract name is ${contractName}`);
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Contract Event Listener

Listens events emitted in contract.

contract.on(`event`, `listener`);
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Example:

contract.on("TransferedFrom", (from, to) => {
    console.log(`Token transfered from ${from} to ${to}`);
});

contract.on("Minted", (tokenId) => {
    console.log(`Token #${tokenId} minted`);
});
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Convert (Ether -> Wei)

Returns BigNumber.

const wei = ethers.utils.parseEther(`ETH`);
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Example:

const weiBigNumber = ethers.utils.parseEther("0.2");
const wei = weiBigNumber.toString();

console.log("wei: ", wei);
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Convert (Wei -> Ether)

Returns string.

const ether = ethers.utils.formatEther(`wei`);
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Example:

const address = "0x28d319067E209fa43Ef46bF54343Dae4CEDd3824";
const balanceBigNumber = await ethers.providers.getBalance(address);

const balance = ethers.utils.formatEther(balanceBigNumber.toString());
console.log(`user balance: ${balance} Ether`);
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Install 

npm install ethers
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Import

for CommonJS

const { ethers } = require('ethers');
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for ES Modules

import { ethers } from 'ethers';
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Network & Chain ID

Gets a connecting network and chain ID.

const network = await provider.getNetwork();
const chainId = network.chainId;
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Example:

// Connect web3
const provider = new ethers.providers.Web3Provider(window.ethereum);

const network = await provider.getNetwork();
const chainId = network.chainId;
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Chain ID List for example:

Chain ID Network
1 Mainnet
3 Ropsten
4 Rinkeby
5 Goerli
10 Optimism
42 Kovan
56 BSC
137 Polygon
42161 Arbitrum One
43114 Avalanche

Top comments (15)

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mmajudith profile image
mmajudith •

Nice write up. Please did you know how i can validate erc721 token ID input field with ether.js?

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hideckies profile image
hideckies •

Thank you. Um...I've never done that so I don't know, sorry.

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nazareth profile image
َ •

Awesome. Btw, for ES Modules -> import { ethers } from 'ethers';
You have a typo there.

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hideckies profile image
hideckies •

Oh thank you. Fixed;)

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ekamkohli profile image
ekamkohli • • Edited

In Convert (Wei -> Ether), const balance = ethers.utils.formatEther(balance.toString());
Please change balance.toString() to balanceBigNumber.toString()

Thanks for providing this cheatsheet.

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hideckies profile image
hideckies •

Oh I was careless. Thank you so much!

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baqirnekfar profile image
NekfarBaqir • • Edited

I have connected with window.ethereum.request function and now I have a disconnect button, how can I do that?

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0xrajkumar profile image
Rajkumar •

How we can write using rpc only ?

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hideckies profile image
hideckies •

If you implement only with RPC, probably can't change states on blockchain.

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0xrajkumar profile image
Rajkumar •

OK

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0xrajkumar profile image
Rajkumar •

We can but we need private to do that, btw thanks

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kelviniot profile image
KelvinIOT •

This is soo comprehensive & helpful, thanks for sharing man.... Also is it possible to call a contract in ethersJS without passing in the provider?

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hideckies profile image
hideckies •

Thanks! You can do this by connecting from your wallet and passing the signer in parameter when initializing a new contract.

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dawsonbotsford profile image
Daws Bot •

Strong list! To help folks even further, let's list all the popular chains you might need to connect to with their ID's:

Polygon: 137
Arbitrum One: 42161
Optimism: 10
Avalanche: 43114
BSC: 56

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hideckies profile image
hideckies •

Thanks! Added them;)

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