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 { ApiRx } = require('@polkadot/api');
const { switchMap } = require('rxjs/operators');

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
  new ApiRx().isReady
    .pipe(
      switchMap((api) =>
        api.rpc.chain.subscribeNewHead()
      ))
    .subscribe((header) => {
      console.log(`Chain is at block: #${header.blockNumber}`);
    });
}

main().catch(console.error);