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# Get Filter Changes \[filter.getChanges]

Returns the changes for a filter since it was created or last polled.

Block and transaction filters return hashes. Event filters return logs.

## Usage

This example returns the changes for a filter since it was created or last polled.

:::code-group
```ts twoslash [example.ts]
import { Actions } from 'viem'
import { client } from './viem.config'

const filter = await client.block.createFilter()

const changes = await client.filter.getChanges({ filter })
// @log: [
// @log:   '0x89644bbd5c8d682a2e9611170e6c1f02573d866d286f006cbf517eec7254ec2d',
// @log: ]
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
import { Client, http, publicActions } from 'viem'
import { mainnet } from 'viem/chains'

export const client = Client.create({
  chain: mainnet,
  transport: http(),
}).extend(publicActions())
```
:::

### Standalone Action

Call `Actions.filter.getChanges` directly by passing the Client as the first argument.

:::code-group
```ts twoslash [example.ts]
import { Actions } from 'viem'
import { client } from './viem.config'

const filter = await Actions.block.createFilter(client)

const changes = await Actions.filter.getChanges(client, { filter })
// @log: [
// @log:   '0x89644bbd5c8d682a2e9611170e6c1f02573d866d286f006cbf517eec7254ec2d',
// @log: ]
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
import { Client, http } from 'viem'
import { mainnet } from 'viem/chains'

export const client = Client.create({
  chain: mainnet,
  transport: http(),
})
```
:::

## Recipes

Use a Client method or pass the Client to the standalone action.

### Polling Block Filters

Use a `block` filter to retrieve block hashes since the previous poll.

```ts twoslash
import { Actions, Client, http } from 'viem'
import { mainnet } from 'viem/chains'

const client = Client.create({ chain: mainnet, transport: http() })
const filter = await Actions.block.createFilter(client)

const blockHashes = await Actions.filter.getChanges(client, { filter }) // [!code focus]
//    ^?
```

### Polling Transaction Filters

Use a `transaction` filter to retrieve pending transaction hashes since the previous poll.

```ts twoslash
import { Actions, Client, http } from 'viem'
import { mainnet } from 'viem/chains'

const client = Client.create({ chain: mainnet, transport: http() })
const filter = await Actions.transaction.createPendingFilter(client)

const transactionHashes = await Actions.filter.getChanges(client, { filter }) // [!code focus]
//    ^?
```

### Polling Event Filters

Use an `event` filter to retrieve decoded event logs since the previous poll.

```ts twoslash
import { Actions, Client, http } from 'viem'
import { mainnet } from 'viem/chains'
import { AbiEvent } from 'viem/utils'

const client = Client.create({ chain: mainnet, transport: http() })
const filter = await Actions.event.createFilter(client, {
  address: '0xfba3912ca04dd458c843e2ee08967fc04f3579c2',
  event: AbiEvent.from(
    'event Transfer(address indexed from, address indexed to, uint256 value)',
  ),
})

const logs = await Actions.filter.getChanges(client, { filter }) // [!code focus]
//    ^?
```

## Return Value

`readonly Hex[] | readonly Log[]`

The changes for the filter. `block` and `transaction` filters return hashes. `event` filters return logs, decoded by `filter.abiEvent` when provided.

## Parameters

### filter

* **Type:** `Actions.filter.Filter`

The filter to poll. Its `request` function must use the transport that created the filter ID.

```ts twoslash
import { Actions, Client, http } from 'viem'
import { mainnet } from 'viem/chains'

const client = Client.create({ chain: mainnet, transport: http() })
// ---cut---
const filter = await Actions.block.createFilter(client) // [!code focus]

const changes = await Actions.filter.getChanges(client, { filter })
```