watchBlockNumber

Action that watches for block number changes.

Import

import { watchBlockNumber } from '@wagmi/core'

Usage

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  onBlockNumber(blockNumber) {
    console.log('Block number changed!', blockNumber)
  },
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

Parameters

import { type WatchBlockNumberParameters } from '@wagmi/core'

chainId

config['chains'][number]['id'] | undefined

ID of chain to use when fetching data.

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { mainnet } from '@wagmi/core/chains'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  chainId: mainnet.id, 
  onBlockNumber(blockNumber) {
    console.log('Block number changed!', blockNumber)
  },
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

emitOnBegin

boolean | undefined

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

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  emitOnBegin: true, 
  onBlockNumber(blockNumber) {
    console.log('Block number changed!', blockNumber)
  },
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

emitMissed

boolean | undefined

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

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  emitMissed: true, 
  onBlockNumber(blockNumber) {
    console.log('Block number changed!', blockNumber)
  },
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

onBlockNumber

(blockNumber: bigint, prevBlockNumber: bigint | undefined) => void

Callback for when block number changes.

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  onBlockNumber(blockNumber) { 
    console.log('Block number changed!', blockNumber) 
  }, 
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

onError

((error: Error) => void) | undefined

Error thrown from getting the block number.

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  onBlockNumber(blockNumber) { 
    console.log('Block number changed!', blockNumber) 
  }, 
  onError(error) { 
    console.error('Block number error', error) 
  }, 
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

poll

boolean | undefined

• Whether or not to use a polling mechanism to check for new blocks instead of a WebSocket subscription.
• Defaults to false for WebSocket Clients, and true for non-WebSocket Clients.

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  onBlockNumber(blockNumber) { 
    console.log('Block number changed!', blockNumber) 
  }, 
  poll: true, 
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

pollingInterval

number | undefined

• Polling frequency (in milliseconds).
• Defaults to the Config's pollingInterval config.

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  onBlockNumber(blockNumber) { 
    console.log('Block number changed!', blockNumber) 
  }, 
  pollingInterval: 1_000, 
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

syncConnectedChain

boolean | undefined

• Set up subscriber for connected chain changes.
• Defaults to Config['syncConnectedChain'].

index.ts

import { watchBlockNumber } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlockNumber(config, {
  onBlockNumber(blockNumber) {
    console.log('Block number changed!', blockNumber)
  },
  syncConnectedChain: false, 
})
unwatch()

config.ts

import { http, createConfig } from '@wagmi/core'
import { mainnet, sepolia } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [mainnet, sepolia],
  transports: {
    [mainnet.id]: http(),
    [sepolia.id]: http(),
  },
})

Return Type

import { type WatchBlockNumberReturnType } from '@wagmi/core'

Function for cleaning up watcher.

Viem

• watchBlockNumber