Metamask: How to prepare a server-side transaction and sign it on the front-end?

Preparing a Transaction with Metamask: A Step-by-Step Guide

Metamask is a popular decentralized application (dApp) tool that enables users to interact with blockchain networks without the need for traditional wallets. One of the most crucial aspects of using Metamask is preparing transactions, which involves sending funds between accounts on different blockchain networks. In this article, we’ll explore how to prepare a transaction from the server and sign it in the front-end using Metamask.

Preparing a Transaction with Metamask

To prepare a transaction with Metamask, you need to follow these steps:

Step 1: Get the User’s Ethereum Address

First, you need to get the user’s Ethereum address. This can be done by checking if they are logged in or have installed the MetaMask browser extension.

const ethereumAddress = window.ethereum.selectedAddress || null;

If Metamask is not installed or the user has not logged in, ethereumAddress will be null.

Step 2: Get the Transaction Details

Next, you need to get the transaction details, including the amount of funds being transferred and the recipient’s Ethereum address.

const transactionDetails = await window.ethereum.selectedAccount.getTransactionDetails();

const amount = transactionDetails.amount;

const recipientAddress = transactionDetails.recipient;

Step 3: Prepare the Transaction

Now that you have the user’s Ethereum address, the transaction details, and the recipient’s Ethereum address, you can prepare the transaction.

const transaction = {

  from: ethereumAddress,

  to: recipientAddress,

  amount: amount,

  gasPrice: await window.ethereum.selectedAccount.getGasPrice(),

  gasLimit: await window.ethereum.selectedAccount.getGasLimit(),

};

Step 4: Send the Transaction (Optional)

If you want to send the transaction, you need to call the sendTransaction method on the window.ethereum.selectedAccount object.

const signedTransaction = await window.ethereum.selectedAccount.sendTransaction(transaction);

Signing a Transaction with Metamask

Once you have prepared the transaction and sent it (if applicable), you can sign it using Metamask. Here’s how:

Step 1: Get the User’s MetaMask Account

First, you need to get the user’s MetaMask account.

const metaMaskAccount = window.ethereum.selectedAccount;

Step 2: Sign the Transaction

Next, you can sign the transaction using Metamask. To do this:

metaMaskAccount.signTransaction(transaction);

Waiting for User Input

If you want to wait for the user to sign the transaction from your frontend before running other functions on the server (e.g., updating a database), you need to use JavaScript’s onload event.

Here’s an example of how to do this:

“`javascript

window.addEventListener(‘load’, async () => {

const ethereumAddress = window.ethereum.selectedAddress || null;

if (!ethereumAddress) return;

// Get the transaction details

const transactionDetails = await window.ethereum.selectedAccount.getTransactionDetails();

const amount = transactionDetails.amount;

const recipientAddress = transactionDetails.recipient;

// Prepare the transaction

const transaction = {

from: ethereumAddress,

to: recipientAddress,

amount: amount,

gasPrice: await window.ethereum.selectedAccount.getGasPrice(),

gasLimit: await window.ethereum.selectedAccount.getGasLimit(),

};

// Send the transaction (optional)

if (!transaction.to) return; // If no recipient address is provided

const signedTransaction = await window.ethereum.selectedAccount.sendTransaction(transaction);

// Wait for user input

while (true) {

const signedUserInput = await window.ethereum.