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Retrieve finalized L2 blocks

A finalized L2 block is a block on an L2 blockchain (Linea) that has been confirmed and validated by the L1 blockchain (Ethereum), ensuring its immutability and security.

There are two methods to obtain the current finalized block:

Use the finalized tag​

Use the finalized tag in API calls to specify a block that has been confirmed by the L1 network. For example, here the eth_getBlockByNumber method returns information about the current finalized block:

curl https://rpc.linea.build \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["finalized",false],"id":1}'

Supported methods​

The finalized tag is supported by all applicable JSON-RPC API methods on Linea Mainnet and Linea Sepolia with the exception of eth_call.

Query the rollup contract​

Using the finalized tag in JSON-RPC API calls is recommended. As an alternative, you can query the Linea L1 rollup contract to retrieve the value of the current finalized L2 block number stored in the currentL2BlockNumber variable.

Prerequisites​

Create the script​

  1. In your project folder, initialize the project and install the web3 package:

    npm init -y
    npm install web3

  2. Create a JavaScript file (for example index.js) and copy the following code:

    Update the Infura endpoint with your API key, or add a different RPC

    provider. :::

    index.js
    const { Web3 } = require("web3")

    // Connect to an Ethereum node (e.g., Infura)
    const web3 = new Web3(
      new Web3.providers.HttpProvider(
        `https://mainnet.infura.io/v3/<YOUR-API-KEY>`
      )
    )
    // Define the minimal ABI to obtain the current finalized block number
    const lineaRollupAbi = [
      {
        "constant": true,
        "inputs": [],
        "name": "currentL2BlockNumber",
        "outputs": [
          {
            "name": "",
            "type": "uint256"
          }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
      }
    ];

    // Define the contract address
    const lineaRollupAddress = '0xd19d4b5d358258f05d7b411e21a1460d11b0876f';

    // Create a contract instance
    const lineaRollupContract = new web3.eth.Contract(lineaRollupAbi, lineaRollupAddress);

    // Function to get the finalized L2 block number
    async function getFinalizedL2BlockNumber() {
      try {
        const currentL2BlockNumber = await lineaRollupContract.methods.currentL2BlockNumber().call();
        const blockNumberHex = '0x' + BigInt(currentL2BlockNumber).toString(16); // Convert BigInt to hex string

        console.log('Finalized L2 Block Number:', currentL2BlockNumber.toString()); // Print BigInt as string
        console.log('Finalized L2 Block Number (Hex):', blockNumberHex);

        return { blockNumber: currentL2BlockNumber, blockNumberHex };
      } catch (error) {
        console.error('Error fetching L2 block number:', error);
      }
    }

    // Call the function
    getFinalizedL2BlockNumber();

  3. In the project directory, run the script:

    node index.js