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Unsubscribe from listening to updates

This example shows how to subscribe to and later unsubscribe from listening to block updates.

In this example we're calling the built-in unsubscribe() function after a timeOut of 20s to cleanup and unsubscribe from listening to updates.

// Import the API
const { ApiPromise } = require('@polkadot/api');
async function main () {
// Create a new instance of the api
const api = await ApiPromise.create();
// Subscribe to chain updates and log the current block number on update.
const unsubscribe = await api.rpc.chain.subscribeNewHeads((header) => {
console.log(`Chain is at block: #${header.number}`);
// In this example we're calling the unsubscribe() function that is being
// returned by the api call function after 20s.
setTimeout(() => {
}, 20000);