Listen to new blocks

This example shows how to subscribe to new blocks.

It displays the block number every time a new block is seen by the node you are connected to.

NOTE: The example runs until you stop it with CTRL+C

// Import the API

const { ApiPromise } = require('@polkadot/api');

async function main () {

// Here we don't pass the (optional) provider, connecting directly to the default

// node/port, i.e. `ws://127.0.0.1:9944`. Await for the isReady promise to ensure

// the API has connected to the node and completed the initialisation process

const api = await ApiPromise.create();

// We only display a couple, then unsubscribe

let count = 0;

// Subscribe to the new headers on-chain. The callback is fired when new headers

// are found, the call itself returns a promise with a subscription that can be

// used to unsubscribe from the newHead subscription

const unsubscribe = await api.rpc.chain.subscribeNewHeads((header) => {

console.log(`Chain is at block: #${header.number}`);

if (++count === 256) {

unsubscribe();

process.exit(0);

}

});

}

main().catch(console.error);