WTF Ethers: 15. Batch Transfer

I've been revisiting ethers.js recently to refresh my understanding of the details and to write a simple tutorial called "WTF Ethers" for beginners.

Twitter: @0xAA_Science

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All the code and tutorials are open-sourced on GitHub: github.com/WTFAcademy/WTF-Ethers

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In this lesson, we will introduce how to perform batch transfers using ethers.js. By calling the Airdrop contract from the WTF Solidity 33: Airdrop, we can achieve batch transfers in a single transaction, saving gas fees.

Airdrop Contract

Here is a brief introduction to the Airdrop contract, you can find the details in the WTF Solidity tutorial. We will mainly use 2 functions:

• multiTransferETH(): Batch transfers of ETH, including 2 parameters:

  • _addresses: An array of user addresses to receive the airdrop (address[] type)
  • _amounts: An array of the token amounts corresponding to each address in _addresses (uint[] type)

• multiTransferToken(): Batch transfers of ERC20 tokens, including 3 parameters:

  • _token: The address of the token contract (address type)
  • _addresses: An array of user addresses to receive the airdrop (address[] type)
  • _amounts: An array of the token amounts corresponding to each address in _addresses (uint[] type)

We have deployed an Airdrop contract on the Goerli testnet, with the address:

0x71C2aD976210264ff0468d43b198FD69772A25fa

Batch Transfer

Next, we will write a script that calls the Airdrop contract to transfer ETH (native token) and WETH (ERC20 token) to 20 addresses.

1. Create an HD wallet to generate addresses in bulk.

   console.log("\n1. Create an HD wallet");
   // Generate an HD wallet from the mnemonic
   const mnemonic = `air organ twist rule prison symptom jazz cheap rather dizzy verb glare jeans orbit weapon universe require tired sing casino business anxiety seminar hunt`;
   const hdNode = ethers.HDNodeWallet.fromPhrase(mnemonic);
   console.log(hdNode);
   

2. Use the HD wallet to generate 20 wallet addresses.

   console.log("\n2. Derive 20 wallet addresses from the HD wallet");
   const numWallet = 20;
   // Derivation path: m / purpose' / coin_type' / account' / change / address_index
   // We only need to change the last part, address_index, to derive new wallets from hdNode
   let basePath = "m/44'/60'/0'/0";
   let addresses = [];
   for (let i = 0; i < numWallet; i++) {
       let hdNodeNew = hdNode.derivePath(basePath + "/" + i);
       let walletNew = new ethers.Wallet(hdNodeNew.privateKey);
       addresses.push(walletNew.address);
   }
   console.log(addresses);
   const amounts = Array(20).fill(ethers.parseEther("0.0001"));
   console.log(`Amounts to send: ${amounts}`);
   

3. Create a provider and wallet for token transfers.

   // Provide the Alchemy API, you can refer to https://github.com/AmazingAng/WTF-Solidity/blob/main/Topics/Tools/TOOL04_Alchemy/readme.md 
   const ALCHEMY_GOERLI_URL = 'https://eth-goerli.alchemyapi.io/v2/GlaeWuylnNM3uuOo-SAwJxuwTdqHaY5l';
   const provider = new ethers.JsonRpcProvider(ALCHEMY_GOERLI_URL);
   
   // Create a wallet object from the private key and provider
   // If this wallet is out of Goerli testnet ETH
   // Please use your own testnet wallet, wallet address: 0x338f8891D6BdC58eEB4754352459cC461EfD2a5E, please don't send any ETH to this address
   // Note: Do not upload your private key to GitHub
   const privateKey = '0x21ac72b6ce19661adf31ef0d2bf8c3fcad003deee3dc1a1a64f5fa3d6b049c06';
   const wallet = new ethers.Wallet(privateKey, provider);

4. Create the Airdrop contract.

   // Airdrop ABI
   const abiAirdrop = [
       "function multiTransferToken(address,address[],uint256[]) external",
       "function multiTransferETH(address[],uint256[]) public payable",
   ];
   // Airdrop contract address (Goerli testnet)
   const addressAirdrop = '0x71C2aD976210264ff0468d43b198FD69772A25fa'; // Airdrop Contract
   // Instantiate the Airdrop contract
   const contractAirdrop = new ethers.Contract(addressAirdrop, abiAirdrop, wallet);

5. Create the WETH contract.

   // WETH ABI
   const abiWETH = [
       "function balanceOf(address) public view returns(uint)",
       "function transfer(address, uint) public returns (bool)",
       "function approve(address, uint256) public returns (bool)"
   ];
   // WETH contract address (Goerli testnet)
   const addressWETH = '0xB4FBF271143F4FBf7B91A5ded31805e42b2208d6'; // WETH Contract
   // Instantiate the WETH contract
   const contractWETH = new ethers.Contract(addressWETH, abiWETH, wallet);

6. Read the ETH and WETH balances for an address.

   ```js
   console.log("\n3. Read the ETH and WETH balances for an address");
   // Read the WETH balance for an address
   const balanceWETH = await contractWETH.balanceOf(addresses[10])
   console.log(`WETH balance: ${ethers.formatEther(balanceWETH)}\n`)
   // Fetch ETH balance
   const balanceETH = await provider.getBalance(addresses[10])
   console.log(`ETH balance: ${ethers.formatEther(balanceETH)}\n`)
   ```
   

7. Call the multiTransferETH() function to transfer 0.0001 ETH to each wallet, and observe the changes in the balances.

   ```js
   console.log("\n4. Call the multiTransferETH() function to transfer 0.0001 ETH to each wallet")
   // Initiate the transaction
   const tx = await contractAirdrop.multiTransferETH(addresses, amounts, {value: ethers.parseEther("0.002")})
   // Wait for the transaction to be mined
   await tx.wait()
   // console.log(`Transaction details:`)
   // console.log(tx)
   const balanceETH2 = await provider.getBalance(addresses[10])
   console.log(`ETH balance of this wallet after the transfer: ${ethers.formatEther(balanceETH2)}\n`)
   ```
   

8. Call the multiTransferToken() function to transfer 0.0001 WETH to each wallet, and observe the changes in the balances.

   ```js
   console.log("\n5. Call the multiTransferToken() function to transfer 0.001 WETH to each wallet")
   // Approve WETH to the Airdrop contract first
   const txApprove = await contractWETH.approve(addressAirdrop, ethers.parseEther("1"))
   await txApprove.wait()
   // Initiate the transaction
   const tx2 = await contractAirdrop.multiTransferToken(addressWETH, addresses, amounts)
   // Wait for the transaction to be mined
   await tx2.wait()
   // console.log(`Transaction details:`)
   // console.log(tx2)
   // Fetch the WETH balance
   const balanceWETH2 = await contractWETH.balanceOf(addresses[10])
   console.log(`WETH balance of this wallet after the transfer: ${ethers.formatEther(balanceWETH2)}\n`)
   ```
   

Summary

In this tutorial, we learned how to use ethers.js to call the Airdrop contract for batch transfers. In the examples, we sent ETH and WETH to 20 different addresses, saving time and gas fees.