Ethers.js

When using Ethers.js on Celo, we suggest using the Celo Ethers.js Wrapper to make Ethers.JS compatible with the Celo network. This means being able to handle fee abstraction when opened in MiniPay/ Valora.

Fee Abstraction on Celo enables the use of stablecoins like cUSD, USDT and USDC as gas tokens.

Celo Ethers.JS Wrapper

A minimal wrapper to make Ethers.JS compatible with the Celo network.

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This is still experimental. View on GitHub

Install

npm i @celo-tools/celo-ethers-wrapper

or

yarn add @celo-tools/celo-ethers-wrapper

Note this wrapper has Ethers v5 as a peer dependency. Your project must include a dependency on that as well.

Basic Usage

Connect to the network by creating a CeloProvider, which is based on JsonRpc-Provider:

import { CeloProvider } from "@celo-tools/celo-ethers-wrapper";

// Connecting to Celo Sepolia testnet
const provider = new CeloProvider("https://forno.celo-sepolia.celo-testnet.org/");
await provider.ready;

Note: for a more efficient provider based on StaticJsonRpcProvider you can use StaticCeloProvider instead.

Next, Create a CeloWallet, which is based on Wallet :

import { CeloWallet } from "@celo-tools/celo-ethers-wrapper";

const wallet = new CeloWallet(YOUR_PK, provider);

Use the provider or wallet to make calls or send transactions:

const txResponse = await wallet.sendTransaction({
  to: recipient,
  value: amountInWei,
});
const txReceipt = await txResponse.wait();
console.info(`CELO transaction hash received: ${txReceipt.transactionHash}`);

Contract Interaction

CeloWallet can be used to send transactions.

Here’s an example of sending cUSD with the Mento StableToken contract. For interacting with contracts you need the ABI and address. Addresses for Celo core contracts can be found with the CLI’s network:contracts command. The ABIs can be built from the solidity code or extracted in ContractKit’s generated folder.

import { Contract, ethers, utils, providers } from "ethers";

const stableToken = new ethers.Contract(address, abi, wallet);
console.info(`Sending ${amountInWei} cUSD`);
const txResponse: providers.TransactionResponse =
  await stableToken.transferWithComment(recipient, amountInWei, comment);
const txReceipt = await txResponse.wait();
console.info(`cUSD payment hash received: ${txReceipt.transactionHash}`);

Alternative gas fee currencies

The Celo network supports paying for transactions with the native asset (CELO) but also with the Mento stabletoken (cUSD).

This wrapper currently has partial support for specifying feeCurrency in transactions.

const gasPrice = await wallet.getGasPrice(stableTokenAddress);
const gasLimit = await wallet.estimateGas(tx);

// Gas estimation doesn't currently work properly for non-CELO currencies
// The gas limit must be padded to increase tx success rate
// TODO: Investigate more efficient ways to handle this case
const adjustedGasLimit = gasLimit.mul(10);

const txResponse = await signer.sendTransaction({
  ...tx,
  gasPrice,
  gasLimit: adjustedGasLimit,
  feeCurrency: stableTokenAddress,
});