useWatchBlockNumber

Hook that watches for block number changes.

Import

import { useWatchBlockNumber } from 'wagmi'

Usage

index.tsx

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    onBlockNumber(blockNumber) {
      console.log('Block number changed!', blockNumber)
    },
  })
}

config.ts

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

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

Parameters

import { type UseWatchBlockNumberParameters } from 'wagmi'

chainId

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

ID of chain to watch blocks at.

index.ts

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    chainId: 1, 
    onBlockNumber(blockNumber) {
      console.log('New block number', blockNumber)
    },
  })
}

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(),
  },
})

config

Config | undefined

Config to use instead of retrieving from the from nearest WagmiProvider.

index.ts

import { useWatchBlockNumber } from 'wagmi'
import { config } from './config'

function App() {
  useWatchBlockNumber({
    config, 
    onBlockNumber(blockNumber) {
      console.log('New block number', blockNumber)
    },
  })
}

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

Whether or not to emit missed blocks to the callback. Defaults to false.

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

index.ts

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    emitMissed: true, 
    onBlockNumber(blockNumber) {
      console.log('New block number', blockNumber)
    },
  })
}

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

Whether or not to emit the block to the callback when the subscription opens. Defaults to false.

index.ts

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    emitOnBegin: true, 
    onBlockNumber(blockNumber) {
      console.log('New block number', blockNumber)
    },
  })
}

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(),
  },
})

enabled

boolean

Whether or not to watch for blocks. Defaults to true.

index.ts

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    enabled: false, 
    onBlockNumber(blockNumber) {
      console.log('New block number', blockNumber)
    },
  })
}

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

(block: Block, prevblock: Block | undefined) => void

Callback for when block changes.

index.ts

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    onBlockNumber(blockNumber) { 
      console.log('New block number', blockNumber) 
    }, 
  })
}

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.

index.ts

import { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    onBlockNumber(blockNumber) { 
      console.log('New block number', blockNumber) 
    }, 
    onError(error) { 
      console.error('Block error', error) 
    }, 
  })
}

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 { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    onBlockNumber(blockNumber) { 
      console.log('New block number', blockNumber) 
    }
    poll: true, 
  })
}

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 { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    onBlockNumber(blockNumber) { 
      console.log('New block number', blockNumber) 
    }
    pollingInterval: 1_000, 
  })
}

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 { useWatchBlockNumber } from 'wagmi'

function App() {
  useWatchBlockNumber({
    onBlockNumber(blockNumber) { 
      console.log('New block number', blockNumber) 
    }
    syncConnectedChain: false, 
  })
}

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 UseWatchBlockNumberReturnType } from 'wagmi'

Function for cleaning up watcher.

Action

• watchBlockNumber