watchBlockNumber #

Watches and returns incoming block numbers.

Usage #

Pass through your Public Client, along with a listener.

import { publicClient } from './client'

const unwatch = publicClient.watchBlockNumber( 
  { onBlockNumber: blockNumber => console.log(blockNumber) }
)
/**
 * > 69420n
 * > 69421n
 * > 69422n
 */

import { createPublicClient, http } from 'viem'
import { mainnet } from 'viem/chains'

export const publicClient = createPublicClient({
  chain: mainnet,
  transport: http()
})

Listener #

(blockNumber: bigint) => void

The block number.

Returns #

UnwatchFn

A function that can be invoked to stop watching for new block numbers.

Parameters #

emitMissed (optional) #

• Type: boolean
• Default: false

Whether or not to emit missed block numbers to the callback.

Missed block numbers may occur in instances where internet connection is lost, or the block time is lesser than the polling interval of the client.

const unwatch = publicClient.watchBlockNumber(
  { 
    emitMissed: true, 
    onBlockNumber: blockNumber => console.log(blockNumber),
  }
)

emitOnBegin (optional) #

• Type: boolean
• Default: false

Whether or not to emit the latest block number to the callback when the subscription opens.

const unwatch = publicClient.watchBlockNumber(
  { 
    emitOnBegin: true, 
    onBlockNumber: blockNumber => console.log(blockNumber),
  }
)

pollingInterval (optional) #

• Type: number

Polling frequency (in ms). Defaults to Client's pollingInterval config.

const unwatch = publicClient.watchBlockNumber(
  { 
    onBlockNumber: blockNumber => console.log(blockNumber),
    pollingInterval: 12_000, 
  }
)

Example #

Check out the usage of watchBlockNumber in the live Watch Block Numbers Example below.

JSON-RPC Methods #

Calls eth_blockNumber on a polling interval.

Real-time subscriptions (eth_subscribe) coming shortly.