watchEvent

Watches and returns emitted Event Logs.

This Action will batch up all the Event Logs found within the pollingInterval, and invoke them via onLogs.

watchEvent will attempt to create an Event Filter and listen to changes to the Filter per polling interval, however, if the RPC Provider does not support Filters (ie. eth_newFilter), then watchEvent will fall back to using getLogs instead.

Usage

By default, you can watch all broadcasted events to the blockchain by just passing onLogs.

These events will be batched up into Event Logs and sent to onLogs:

example.tsclient.ts

import { publicClient } from './client'
import { wagmiAbi } from './abi'

const unwatch = await publicClient.watchEvent({
  onLogs: logs => console.log(logs)
})
// > [{ ... }, { ... }, { ... }]
// > [{ ... }, { ... }]
// > [{ ... }, { ... }, { ... }, { ... }]

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

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

Scoping

You can also scope watchEvent to a set of given attributes (listed below).

Address

watchEvent can be scoped to an address:

example.tsclient.ts

import { publicClient } from './client'
import { wagmiAbi } from './abi'

const unwatch = await publicClient.watchEvent({
  address: '0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48', 
  onLogs: logs => console.log(logs)
})
// > [{ ... }, { ... }, { ... }]
// > [{ ... }, { ... }]
// > [{ ... }, { ... }, { ... }, { ... }]

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

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

Event

watchEvent can be scoped to an event.

The event argument takes in an event in ABI format – we have a parseAbiItem utility that you can use to convert from a human-readable event signature → ABI.

example.tsclient.ts

import { parseAbiItem } from 'viem' 
import { publicClient } from './client'
import { wagmiAbi } from './abi'

const unwatch = await publicClient.watchEvent({
  address: '0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48',
  event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'), 
  onLogs: logs => console.log(logs)
})
// > [{ ... }, { ... }, { ... }]
// > [{ ... }, { ... }]
// > [{ ... }, { ... }, { ... }, { ... }]

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

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

By default, event accepts the AbiEvent type:

import { publicClient } from '.'

const unwatch = await publicClient.watchEvent(publicClient, {
  address: '0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48',
  event: { 
    name: 'Transfer', 
    inputs: [
      { type: 'address', indexed: true, name: 'from' },
      { type: 'address', indexed: true, name: 'to' },
      { type: 'uint256', indexed: false, name: 'value' }
    ] 
  },
  onLogs: logs => console.log(logs)
})

Arguments

watchEvents can be scoped to given indexed arguments on the event:

example.tsclient.ts

import { parseAbiItem } from 'viem'
import { publicClient } from './client'

const unwatch = await publicClient.watchEvent({
  address: '0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48',
  event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'),
  args: { 
    from: '0xd8da6bf26964af9d7eed9e03e53415d37aa96045',
    to: '0xa5cc3c03994db5b0d9a5eedd10cabab0813678ac'
  },
  onLogs: logs => console.log(logs)
})
// > [{ ... }, { ... }, { ... }]
// > [{ ... }, { ... }]
// > [{ ... }, { ... }, { ... }, { ... }]

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

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

Only indexed arguments in event are candidates for args.

These arguments can also be an array to indicate that other values can exist in the position:

const unwatch = await publicClient.watchEvent({
  address: '0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48',
  event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'),
  args: { 
    // '0xd8da...' OR '0xa5cc...' OR '0xa152...'
    from: [
      '0xd8da6bf26964af9d7eed9e03e53415d37aa96045', 
      '0xa5cc3c03994db5b0d9a5eedd10cabab0813678ac',
      '0xa152f8bb749c55e9943a3a0a3111d18ee2b3f94e',
    ],
  }
  onLogs: logs => console.log(logs)
})

Returns

UnwatchFn

A function that can be invoked to stop watching for new Event Logs.

Parameters

onLogs

Type: (logs: Log[]) => void

The new Event Logs.

const unwatch = publicClient.watchEvent(
  { onLogs: logs => console.log(logs) } 
)

address (optional)

Type: Address | Address[]

The contract address or a list of addresses from which Logs should originate.

const unwatch = publicClient.watchEvent(
  { 
    address: '0xfba3912ca04dd458c843e2ee08967fc04f3579c2', 
    onLogs: logs => console.log(logs) 
  }
)

event (optional)

Type: AbiEvent

The event in ABI format.

A parseAbiItem utility is exported from viem that converts from a human-readable event signature → ABI.

import { parseAbiItem } from 'viem' 

const unwatch = publicClient.watchEvent(
  { 
    address: '0xfba3912ca04dd458c843e2ee08967fc04f3579c2',
    event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'), 
    onLogs: logs => console.log(logs) 
  }
)

args (optional)

Type: Inferred.

A list of indexed event arguments.

const unwatch = publicClient.watchEvent(
  { 
    address: '0xfba3912ca04dd458c843e2ee08967fc04f3579c2',
    event: parseAbiItem('event Transfer(address indexed from, address indexed to, uint256 value)'),
    args: { 
     from: '0xd8da6bf26964af9d7eed9e03e53415d37aa96045',
      to: '0xa5cc3c03994db5b0d9a5eedd10cabab0813678ac'
    }
    onLogs: logs => console.log(logs) 
  }
)

batch (optional)

Type: boolean
Default: true

Whether or not to batch the Event Logs between polling intervals.

const unwatch = publicClient.watchEvent(
  { 
    batch: false, 
    onLogs: logs => console.log(logs),
  }
)

onError (optional)

Type: (error: Error) => void

Error thrown from listening for new Event Logs.

const unwatch = publicClient.watchEvent(
  { 
    onError: error => console.log(error) 
    onLogs: logs => console.log(logs),
  }
)

pollingInterval (optional)

Type: number

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

const unwatch = publicClient.watchEvent(
  { 
    pollingInterval: 1_000, 
    onLogs: logs => console.log(logs),
  }
)

Live Example

Check out the usage of watchEvent in the live Event Logs Example below.

JSON-RPC Methods

RPC Provider supports eth_newFilter:

Calls eth_newFilter to create a filter (called on initialize).
On a polling interval, it will call eth_getFilterChanges.

RPC Provider does not support eth_newFilter:

Calls eth_getLogs on a polling interval.

watchEvent #

Usage #

Scoping #

Address #

Event #

Arguments #

Returns #

Parameters #

onLogs #

address (optional) #

event (optional) #

args (optional) #

batch (optional) #

onError (optional) #

pollingInterval (optional) #

Live Example #

JSON-RPC Methods #

watchEvent

Usage

Scoping

Address

Event

Arguments

Returns

Parameters

onLogs

address (optional)

event (optional)

args (optional)

batch (optional)

onError (optional)

pollingInterval (optional)

Live Example

JSON-RPC Methods