What is Gas?

In Ethereum, gas is a unit that measures the amount of computational effort required to execute operations such as transactions or smart contract executions. Every operation in Ethereum has a gas cost, and users must pay for this gas in Ether (ETH). The total cost of a transaction is determined by the formula: 

Transaction Cost = Gas Used * Gas Price

Gas is essential for preventing spam on the network and ensuring that miners are compensated for their work. If a transaction runs out of gas, it will fail, but the gas used will still be consumed.

Gas Limit

The gas limit is the maximum amount of gas that a user is willing to spend on a transaction. If the transaction requires more gas than the specified limit, it will fail. However, if the transaction uses less gas, the unused gas is refunded.

Specifying Gas Limits in Ethers.js

In Ethers.js, you can specify gas limits when creating a transaction object. Below is a complete HTML example that demonstrates how to specify gas limits when sending Ether using Ethers.js: 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Ethers.js Gas Limit Example</title>
    <script src="https://cdn.jsdelivr.net/npm/ethers@5.7.0/dist/ethers.umd.min.js"></script>
</head>
<body>
    <h1>Send Ether with Gas Limit</h1>
    <input type="text" id="recipientInput" placeholder="Enter recipient address" />
    <input type="number" id="amountInput" placeholder="Enter amount in ETH" />
    <input type="number" id="gasLimitInput" placeholder="Enter gas limit" />
    <input type="text" id="privateKeyInput" placeholder="Enter your private key" />
    <button id="sendButton">Send Ether</button>
    <pre id="transactionInfo"></pre>

    <script>
        async function sendEtherWithGasLimit() {
            const provider = new ethers.providers.Web3Provider(window.ethereum);
            const recipient = document.getElementById('recipientInput').value;
            const amount = document.getElementById('amountInput').value;
            const gasLimit = document.getElementById('gasLimitInput').value;
            const privateKey = document.getElementById('privateKeyInput').value;

            // Create a wallet instance
            const wallet = new ethers.Wallet(privateKey, provider);

            // Create a transaction object
            const tx = {
                to: recipient,
                value: ethers.utils.parseEther(amount), // Convert amount to Wei
                gasLimit: gasLimit ? ethers.BigNumber.from(gasLimit) : undefined // Specify gas limit
            };

            try {
                // Send the transaction
                const transactionResponse = await wallet.sendTransaction(tx);
                document.getElementById('transactionInfo').innerText = "Transaction Sent: " + transactionResponse.hash;

                // Wait for the transaction to be mined
                await transactionResponse.wait();
                document.getElementById ('transactionInfo').innerText += "\\nTransaction Mined: " + transactionResponse.hash;
            } catch (error) {
                document.getElementById('transactionInfo').innerText = "Error: " + error.message;
            }
        }

        document.getElementById('sendButton').onclick = sendEtherWithGasLimit;
    </script>
</body>
</html>

How It Works

In the example above:

  1. We create a simple HTML interface that allows the user to input the recipient's address, the amount of Ether to send, the gas limit, and the sender's private key.
  2. The sendEtherWithGasLimit function initializes a connection to the Ethereum network using a Web3 provider.
  3. A wallet instance is created using the provided private key and the provider.
  4. A transaction object is constructed with the recipient's address, the amount of Ether to send (converted from Ether to Wei), and the specified gas limit.
  5. The transaction is sent using the wallet.sendTransaction method, and the transaction hash is displayed on the webpage.
  6. Finally, the code waits for the transaction to be mined and updates the displayed information accordingly.

Conclusion

Understanding gas and how to specify gas limits in Ethers.js is crucial for interacting with the Ethereum blockchain effectively. By following the steps outlined above, you can ensure that your transactions are executed smoothly and efficiently, while also managing the costs associated with gas.