watchBlocks

Action that watches for block changes.

Import

import { watchBlocks } from '@wagmi/core'

Usage

index.ts

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

const unwatch = watchBlocks(config, {
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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 WatchBlocksParameters } from '@wagmi/core'

blockTag

'latest' | 'earliest' | 'pending' | 'safe' | 'finalized'

Watch for new blocks on a given tag. Defaults to 'latest'.

index.ts

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

const unwatch = watchBlocks(config, {
  blockTag: 'pending', 
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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(),
  },
})

chainId

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

ID of chain to use when fetching data.

index.ts

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

const unwatch = watchBlocks(config, {
  chainId: mainnet.id, 
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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

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

const unwatch = watchBlocks(config, {
  emitMissed: true, 
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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

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

index.ts

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

const unwatch = watchBlocks(config, {
  emitOnBegin: true, 
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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(),
  },
})

onBlock

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

Callback for when block changes.

index.ts

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

const unwatch = watchBlocks(config, {
  onBlock(block) { 
    console.log('Block changed!', block) 
  }, 
})
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.

index.ts

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

const unwatch = watchBlocks(config, {
  onBlock(block) { 
    console.log('Block changed!', block) 
  }, 
  onError(error) { 
    console.error('Block 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 { watchBlocks } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlocks(config, {
  poll: true, 
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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 { watchBlocks } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlocks(config, {
  pollingInterval: 1_000, 
  onBlock(block) {
    console.log('Block changed!', block)
  },
})
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 { watchBlocks } from '@wagmi/core'
import { config } from './config'

const unwatch = watchBlocks(config, {
  onBlock(block) {
    console.log('Block changed!', block)
  },
  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 WatchBlocksReturnType } from '@wagmi/core'

Function for cleaning up watcher.

Viem

• watchBlocks