# Filter
## getFilterChanges
```javascript
caver.klay.getFilterChanges(filterId [, callback])
```
Polling method for a filter, which returns an array of logs since the last poll.
**Parameters**
| Name | Type | Description |
| -------- | -------- | ---------------------------------------------------------------------------------------------------------- |
| filterId | String | The filter id. |
| callback | Function | (optional) Optional callback, returns an error object as the first parameter and the result as the second. |
**Return Value**
`Promise` returns `Array` - Array of log objects, or an empty array if nothing has changed since last poll.
The structure of the returned log `Object` in the `Array` looks as follows:
| Name | Type | Description |
| ---------------- | ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| address | 20-byte DATA | Address from which this log originated. |
| topics | Array of DATA | Array of 0 to 4 32-byte DATA of indexed log arguments. (In Solidity: The first topic is the hash of the signature of the event (*e.g.*, `Deposit(address,bytes32,uint256)`), except you declared the event with the `anonymous` specifier.). |
| data | DATA | Contains the non-indexed arguments of the log. |
| blockNumber | QUANTITY | The block number where this log was in. `null` when pending. |
| transactionHash | 32-byte DATA | Hash of the transaction that this log was created from. `null` when pending, an edge case when the transaction has been executed, but the block has not been confirmed. |
| transactionIndex | QUANTITY | Integer. The index of the transaction that this log was created from. `null` when pending. |
| blockHash | 32-byte DATA | Hash of the block where this log was in. `null` when pending. |
| logIndex | QUANTITY | Integer of the log index position in the block. `null` when it is a pending log. |
| id | String | A log identifier. It is made by concatenating "log\_" string with `keccak256(blockHash + transactionHash + logIndex).substr(0, 8)` |
**Example**
```javascript
> caver.klay.getFilterChanges('0xafb8e49bbcba9d61a3c616a3a312533e').then(console.log);
[
{
address: '0x71e503935b7816757AA0314d4E7354dab9D39162',
topics: [ '0xe8451a9161f9159bc887328b634789768bd596360ef07c5a5cbfb927c44051f9' ],
data: '0x0000000000000000000000000000000000000000000000000000000000000001',
blockNumber: 3525,
transactionHash: '0x1b28e2c723e45a0d8978890598903f36a74397c9cea8531dc9762c39483e417f',
transactionIndex: 0,
blockHash: '0xb7f0bdaba93d3baaa01a5c24517da443207f774e0202f02c298e8e997a540b3d',
logIndex: 0,
id: 'log_c1ea867d'
}
]
```
## getFilterLogs
```javascript
caver.klay.getFilterLogs(filterId [, callback])
```
Returns an array of all logs matching the filter with the given id. The filter object should be obtained using [newFilter](#newfilter).\
Note that filter ids returned by other filter creation functions, such as [newBlockFilter](#newblockfilter) or [newPendingTransactionFilter](#newpendingtransactionfilter), cannot be used with this function.
**Parameters**
| Name | Type | Description |
| -------- | -------- | ---------------------------------------------------------------------------------------------------------- |
| filterId | String | The filter id. |
| callback | Function | (optional) Optional callback, returns an error object as the first parameter and the result as the second. |
**Return Value**
See [getFilterChanges](#getfilterchanges)
**Example**
```javascript
> caver.klay.getFilterLogs('0xcac08a7fc32fc625a519644187e9f690').then(console.log);
[
{
address: '0x55384B52a9E5091B6012717197887dd3B5779Df3',
topics: [ '0xe8451a9161f9159bc887328b634789768bd596360ef07c5a5cbfb927c44051f9' ],
data: '0x0000000000000000000000000000000000000000000000000000000000000001',
blockNumber: 7217,
transactionHash: '0xa7436c54e47dafbce696de65f6e890c96ac22c236f50ca1be28b9b568034c3b3',
transactionIndex: 0,
blockHash: '0xe4f27c524dacfaaccb36735deccee69b3d6c315e969779784c36bb8e14b89e01',
logIndex: 0,
id: 'log_2dd695a8'
}
]
```
## getPastLogs
```javascript
caver.klay.getPastLogs(options [, callback])
```
Gets past logs, matching the given options.
**Parameters**
| Name | Type | Description |
| ----------------- | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| options | Object | The filter options. |
| options.fromBlock | Number \| String | (optional) The number of the earliest block to get the logs. (`"latest"` means the most recent block.) The default value is `"latest"`. |
| options.toBlock | Number \| String | (optional) The number of the last block to get the logs. (`"latest"` means the most recent block.). The default value is `"latest"`. |
| options.address | String \| Array | (optional) An address or a list of addresses. Only the logs related to the particular account(s) will be returned. |
| options.topics | Array | (optional) An array of values that must appear in the log entries. The order is important. If you want to leave topics out, use `null`, *e.g.*, `[null, '0x12...']`. You can also pass an array for each topic with options for that topic, *e.g.,* `[null, ['option1', 'option2']]`. |
| callback | Function | (optional) Optional callback, returns an error object as the first parameter and the result as the second. |
**Return Value**
`Promise` returns `Array` - Array of log objects.
The structure of the returned event `Object` in the `Array` looks as follows:
| Name | Type | Description |
| ---------------- | -------------- | --------------------------------------------------------------------------------------------------------------------------------------- |
| address | String | From which this event originated from. |
| data | String | The data containing non-indexed log parameter. |
| topics | Array | An array with max 4 32-byte topics, topic 1-3 contains indexed parameters of the log. |
| logIndex | Number | Integer of the event index position in the block. |
| transactionIndex | Number | Integer of the transaction's index position, the event was created in. |
| transactionHash | 32-byte String | Hash of the transaction this event was created in. |
| blockHash | 32-byte String | Hash of the block where this event was created in. `null` when its still pending. |
| blockNumber | Number | The block number where this log was created in. `null` when still pending. |
| id | String | A log identifier. It is made through concatenating "log\_" string with `keccak256(blockHash + transactionHash + logIndex).substr(0, 8)` |
**Example**
```javascript
> caver.klay.getPastLogs({
address: "0x11f4d0A3c12e86B4b5F39B213F7E19D048276DAe",
topics: ["0x033456732123ffff2342342dd12342434324234234fd234fd23fd4f23d4234"]
})
.then(console.log);
[{
data: '0x7f9fade1c0d57a7af66ab4ead79fade1c0d57a7af66ab4ead7c2c2eb7b11a91385',
topics: ['0xfd43ade1c09fade1c0d57a7af66ab4ead7c2c2eb7b11a91ffdd57a7af66ab4ead7', '0x7f9fade1c0d57a7af66ab4ead79fade1c0d57a7af66ab4ead7c2c2eb7b11a91385']
logIndex: 0,
transactionIndex: 0,
transactionHash: '0x7f9fade1c0d57a7af66ab4ead79fade1c0d57a7af66ab4ead7c2c2eb7b11a91385',
blockHash: '0xfd43ade1c09fade1c0d57a7af66ab4ead7c2c2eb7b11a91ffdd57a7af66ab4ead7',
blockNumber: 1234,
address: '0xde0B295669a9FD93d5F28D9Ec85E40f4cb697BAe',
id: 'log_124d61bc',
},{...}]
```
## newBlockFilter
```javascript
caver.klay.newBlockFilter([callback])
```
Creates a filter in the node to receive the information about new block arrival. To check if the state has changed, call [getFilterChanges](#getfilterchanges).
**Parameters**
| Name | Type | Description |
| -------- | -------- | ----------------------------------------------------------------------------------------------------------------------------- |
| callback | Function | (optional) Optional callback. The callback is fired with an error object as its first parameter and the result as the second. |
**Return Value**
`Promise` returns `String` - A filter id.
**Example**
```javascript
> caver.klay.newBlockFilter().then(console.log);
0x9ca049dc8b0788ee05724e45fc4137f1
```
## newFilter
```javascript
caver.klay.newFilter(options [, callback])
```
Creates a filter object using the given filter options, to receive the specific state changes (logs).
* To check if the state has changed, call [getFilterChanges](#getfilterchanges).
* To obtain all logs matching the filter created by `newFilter`, call [getFilterLogs](#getfilterlogs).
For detailed information about topic filters, please see [Klaytn Platform API - klay\_newFilter](https://klaytn.gitbook.io/docs/json-rpc/api-references/klay/filter#klay_newfilter).
**Parameters**
| Name | Type | Description |
| ----------------- | ---------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| options | Object | The filter options. |
| options.fromBlock | Number \| String | (optional) The number of the earliest block height to query the events. (There are special tags, `"latest"` means the most recent block). The default value is `"latest"`. |
| options.toBlock | Number \| String | (optional) The number of the last block height to query the events (There are special tags,`"latest"` means the most recent confirmed block). The default value is `"latest"`. |
| options.address | String \| Array | (optional) An address or a list of addresses to get logs generated inside the given contract(s). |
| options.topics | Array | (optional) An array of values to search for in the log entries. The order is important. If you want to match everything in the given position, use `null`, *e.g.*, `[null, '0x12...']`. You can also pass an array to match one of them. *e.g.,* `[null, ['option1', 'option2']]`. |
| callback | Function | (optional) Optional callback, returns an error object as the first parameter and the result as the second. |
**Return Value**
`Promise` returns `String` - A filter id.
**Example**
```javascript
> caver.klay.newFilter({}).then(console.log);
0x40d40cb9758c6f0d99d9c2ce9c0f823
> caver.klay.newFilter({address: "0x55384B52a9E5091B6012717197887dd3B5779Df3"}).then(console.log);
0xd165cbf31b9d60346aada33dbefe01b
```
## newPendingTransactionFilter
```javascript
caver.klay.newPendingTransactionFilter([callback])
```
Creates a filter in the node, to receive the information about new pending transactions arrival. To check if the state has changed, call [getFilterChanges](#getfilterchanges).
**Parameters**
| Name | Type | Description |
| -------- | -------- | ---------------------------------------------------------------------------------------------------------- |
| callback | Function | (optional) Optional callback, returns an error object as the first parameter and the result as the second. |
**Return Value**
`Promise` returns `String` - A filter id.
**Example**
```javascript
> caver.klay.newPendingTransactionFilter().then(console.log);
0x1426438ffdae5abf43edf4159c5b013b
```
## uninstallFilter
```javascript
caver.klay.uninstallFilter(filterId [, callback])
```
Removes the filter with the given id. It is strongly recommended to immediately remove the filter if monitoring is no longer needed. A filter will be removed if the filter has not been invoked through [getFilterChanges](#getfilterchanges) for more than the timeout value set in the node. The default configuration is 5 minutes.
**Parameters**
| Name | Type | Description |
| -------- | -------- | ---------------------------------------------------------------------------------------------------------- |
| filterId | String | The filter id. |
| callback | Function | (optional) Optional callback, returns an error object as the first parameter and the result as the second. |
**Return Value**
`Promise` returns `Boolean` - `true` if the filter was successfully uninstalled, otherwise `false`.
**Example**
```javascript
> caver.klay.uninstallFilter('0x1426438ffdae5abf43edf4159c5b013b').then(console.log);
true
```