eth_newFilter | Avalanche

Avalanche API method that generates a filter object based on the filter parameters. It returns a filter ID, which can be used to retrieve the results of the filter using the eth_getFilterChanges method. By creating a filter for specific events, developers can receive notifications when those events occur and use them to trigger actions in their applications.

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Parameters

• object — the filter parameters:
  • fromBlock — (optional, default: latest) integer that specifies the starting block number from which the logs should be fetched.
  • toBlock — (optional, default: latest) integer that specifies the ending block number until which the logs should be fetched.
  • address — (optional) the contract address from which the logs should be fetched. It can be a single address or an array of addresses.
  • topics — (optional) an array of DATA topics. The event topics for which the logs should be fetched. It can be a single topic or an array of topics.
  • blockhash — (optional) the hash of the specific block. Limits logs to a specific block with a 32-byte hash value. It takes precedence over fromBlock and toBlock.

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Response

• result — a hexadecimal string representing the ID of the newly created filter

Use the following methods with the filter ID:

• eth_getFilterChanges to retrieve updated logs
• eth_uninstallFilter to remove the filter

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eth_newFilter code examples

const ethers = require('ethers');
const NODE_URL = "CHAINSTACK_NODE_URL";
const provider = new ethers.JsonRpcProvider(NODE_URL);

const filter = {
  toBlock: 'latest',
  address: '0x0d500B1d8E8eF31E21C99d1Db9A6444d3ADf1270',
  topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef']
};

const createFilter = async () => {
  try {
    const filterId = await provider.send('eth_newFilter', [filter]);
    console.log(filterId); // the filter ID returned by eth_newFilter
    return filterId
  } catch (error) {
    console.log(error);
  }
};

createFilter();

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Use case

You can use eth_newFilter to create a filter for a specific action on a smart contract, for example, to monitor the transfer transactions from the Wrapped ETH token.

The idea is to create a filter using the eth_newFilter method to monitor an ERC-20 smart contract, WETH in this case.

The following filter parameters are selected:

const filter = {
  // Poll the latest block available
  toBlock: 'latest',	
  
  // WETH smart contract address
  address: '0x49D5c2BdFfac6CE2BFdB6640F4F80f226bc10bAB',
  
  // Signature of the Transfer event.
  topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef'], 
};

The program is then polling the filter every 2 seconds to check for any new changes using the eth_getFilterChanges method.

Here is the implementation using ethers.js:

const ethers = require('ethers');
const NODE_URL = "CHAINSTACK_NODE_URL";
const provider = new ethers.JsonRpcProvider(NODE_URL);

const filter = {
  toBlock: 'latest',
  address: '0x49D5c2BdFfac6CE2BFdB6640F4F80f226bc10bAB',
  topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef'],
};

const createAndPollFilter = async () => {
  try {
    const filterId = await provider.send('eth_newFilter', [filter]);
    console.log(`The filter ID is: ${filterId}`); // the filter ID returned by eth_newFilter

    // Poll the filter every 30 seconds
    setInterval(async () => {
      const filterChanges = await provider.send('eth_getFilterChanges', [filterId]);

      if (filterChanges.length === 0) {
        console.log('No new logs since the last poll.');
      } else {
        console.log(filterChanges); // the filter changes returned by eth_getFilterChanges
      }
    }, 2000); // 2 seconds in milliseconds

    return filterId;
  } catch (error) {
    console.log(error);
  }
};

createAndPollFilter();

Here’s a breakdown of how the code works:

The createAndPollFilter function is an asynchronous function that creates and polls a filter for the WETH smart contract on Avalanche.

The eth_newFilter method creates a new filter with the specified parameters. In this case, it passes in the filter object as the filter parameter. The method returns the ID of the newly created filter, which is then logged into the console.

The setInterval method is used to poll the filter every 2 seconds. It takes a function as the first argument and an interval in milliseconds as the second argument. The function passed to setInterval is an asynchronous function that calls eth_getFilterChanges with the filter ID returned by eth_newFilter. This method returns an array of all the changes to the filter since the last time it was polled. If there are no changes, it logs “No new logs since the last poll.” to the console. If there are changes, it logs the filter changes to the console.

The createAndPollFilter function returns the filter ID, and if there are any errors thrown while creating or polling the filter, the catch block logs the error to the console.