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clearSubscriptions | Ethereum

web3.js method used to unsubscribe from all subscriptions made with the web3.eth.subscribe method. This method is useful for removing all of the subscriptions at once.

The subscriptions available using the web3.eth.subscribe method are:

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Parameters

boolean — keep the subscribe("syncing") subscription if true.

Response

boolean — the boolean value indicating if the subscriptions were removed successfully. true if removed successfully, false if not.

clearSubscriptions code example

const Web3 = require("web3");
const NODE_URL = "CHAINSTACK_WSS_URL";
const web3 = new Web3(NODE_URL);

async function clearSubscriptions() {
    try {
      await web3.eth.clearSubscriptions();
      console.log("Subscriptions were cancelled successfully");
      return process.exit(1)
      
    } catch (error) {
      console.error("Failed to cancel subscriptions:", error);
      return process.exit(1)
    }
  }
  
clearSubscriptions()

Use case

A way to use the clearSubscriptions method is to place it in a timer to clear all of the subscriptions after a pre-determined about.

The following code is an example using the subscribe("newBlockHeaders") method, which will be stopped and removed after one minute using clearSubscriptions:

const Web3 = require("web3");
const NODE_URL = "CHAINSTACK_WSS_URL";
const web3 = new Web3(NODE_URL);

async function subscribeToNewBlocks() {
    try {
        // Create a new subscription to the 'newBlockHeaders' event
        const subscription = await web3.eth.subscribe('newBlockHeaders');

        // Attach event listeners to the subscription object
        subscription.on('connected', handleConnected);
        subscription.on('data', handleNewBlock);
        subscription.on('error', handleError);
    } catch (error) {
        console.error(`Error subscribing to new blocks: ${error}`);
    }
}

/* Fallback functions to react to the different events */

// Event listener that logs a message when the subscription is connected
function handleConnected(subscriptionId) {
    console.log(`New subscription: ${subscriptionId}`);
}

// Event listener that logs the received block header data
function handleNewBlock(blockHeader) {
    console.log(blockHeader);
}

// Event listener that logs any errors that occur
function handleError(error) {
    console.error(`Error receiving new blocks: ${error}`);
}

async function clearSubscriptions() {
    try {
        await web3.eth.clearSubscriptions();
        console.log("Subscriptions were cancelled successfully");
        return process.exit(1)

    } catch (error) {
        console.error("Failed to cancel subscriptions:", error);
        return process.exit(1)
    }
}

async function main() {

    subscribeToNewBlocks();

    // Run clearSubscriptions() once after 60 seconds
    setTimeout(clearSubscriptions, 60000);
}

main()

The code starts by defining an async function called subscribeToNewBlocks that creates a new subscription to the newBlockHeaders event using the web3.eth.subscribe method. This method returns a subscription object that can be used to attach event listeners for different events, such as connected, data, and error. The code defines three event listener functions handleConnected, handleNewBlock, and handleError that log messages to the console when these events occur.

The subscribeToNewBlocks function is called from the main function, which is also defined in the code. The main function calls subscribeToNewBlocks to create a new subscription and then schedules the clearSubscriptions function to run once after 60 seconds using the setTimeout function. The clearSubscriptions function uses the web3.eth.clearSubscriptions method to cancel any existing subscriptions and log a message to the console if the cancellation was successful.