What is Gas Estimation?

Gas estimation is the process of predicting the amount of gas required to execute a transaction or a smart contract function on the Ethereum blockchain. This is important because it helps users set appropriate gas limits and avoid transaction failures due to insufficient gas.

How to Estimate Gas in Ethers.js

Ethers.js provides a method called estimateGas that can be used to estimate the gas required for a transaction. This method can be called on a contract instance or directly on a transaction object. Below is a complete HTML example demonstrating how to estimate gas for a transaction 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 Estimation Example</title>
    <script src="https://cdn.jsdelivr.net/npm/ethers@5.7.0/dist/ethers.umd.min.js"></script>
</head>
<body>
    <h1>Estimate Gas for a Transaction</h1>
    <input type="text" id="contractAddressInput" placeholder="Enter contract address" />
    <input type="text" id="functionNameInput" placeholder="Enter function name" />
    <input type="text" id="paramsInput" placeholder="Enter function parameters (comma-separated)" />
    <button id="estimateButton">Estimate Gas</button>
    <pre id="gasEstimateResult"></pre>

    <script>
        async function estimateGas() {
            const provider = new ethers.providers.Web3Provider(window.ethereum);
            const contractAddress = document.getElementById('contractAddressInput').value;
            const functionName = document.getElementById('functionNameInput').value;
            const params = document.getElementById('paramsInput').value.split(',').map(param => param.trim());

            // Create a contract instance
            const contract = new ethers.Contract(contractAddress, [
                // ABI of the function to estimate gas for
                "function " + functionName + "(" + params.map(() => "uint256").join(", ") + ")"
            ], provider);

            try {
                // Estimate gas
                const gasEstimate = await contract.estimateGas[functionName](...params);
                document.getElementById('gasEstimateResult').innerText = "Estimated Gas: " + gasEstimate.toString();
            } catch (error) {
                document.getElementById('gasEstimateResult').innerText = "Error: " + error.message;
            }
        }

        document.getElementById('estimateButton').onclick = estimateGas;
    </script>
</body>
</html>

How It Works

In the example above:

  1. We create a simple HTML interface that allows the user to input the contract address, the function name, and the parameters for the function.
  2. The estimateGas function initializes a connection to the Ethereum network using a Web3 provider.
  3. A contract instance is created using the provided contract address and a simplified ABI that includes the function to estimate gas for.
  4. The estimateGas method is called on the contract instance with the specified function name and parameters.
  5. The estimated gas is displayed on the webpage, or an error message is shown if the estimation fails.

Conclusion

Estimating gas for transactions in Ethers.js is a crucial step in ensuring that your transactions are executed successfully without running out of gas. By using the estimateGas method, you can predict the gas required for your transactions and set appropriate gas limits, thereby enhancing the efficiency of your interactions with the Ethereum blockchain.