# caver.wallet

`caver.wallet` is a package that manages [Keyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/caver.wallet/keyring) instances in in-memory wallet. `caver.wallet` accepts all [SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring), and [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring), and manages them by address.

## Class <a href="#class" id="class"></a>

### KeyringContainer <a href="#keyringcontainer" id="keyringcontainer"></a>

```javascript
caver.wallet
```

`KeyringContainer` is a class that manages [SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring), and [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring) instances. Caver가 초기화될 때 `caver.wallet` 안에 KeyringContainer 인스턴스를 생성합니다. `caver.wallet`를 통해 인메모리 지갑에 키링 인스턴스를 저장하고 관리할 수 있습니다.

**properties**

| Name   | Type   | Description                     |
| ------ | ------ | ------------------------------- |
| length | number | keyringContainer에 포함된 키링의 수입니다. |

## caver.wallet.generate <a href="#caver-wallet-generate" id="caver-wallet-generate"></a>

```javascript
caver.wallet.generate(numberOfKeyrings [, entropy])
```

Generates instances of [SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring) in the keyringContainer with randomly generated private keys.

**Parameters**

| Name             | Type   | Description                                                                                                                                                  |
| ---------------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| numberOfKeyrings | number | The number of [SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring) instances to create. |
| entropy          | string | (선택 사항) 엔트로피를 증가시키는 임의의 문자열입니다.                                                                                                                              |

**Return Value**

| Type  | Description               |
| ----- | ------------------------- |
| Array | 생성된 인스턴스의 주소를 포함하는 배열입니다. |

**Example**

```javascript
// generate without entropy
> caver.wallet.generate(3)
[
    '0xb4b0c3781082cf818bfaf5adfc73fdf59d92c1cd',
    '0x9957dfd92e4b70f91131c573293343bc5f21f215',
    '0xed2fe179c18fa528da2392532998560bd1008511'
]

// generate with entropy
> caver.wallet.generate(3, caver.utils.randomHex(32))
[
    '0xb4b0c3781082cf818bfaf5adfc73fdf59d92c1cd',
    '0x9957dfd92e4b70f91131c573293343bc5f21f215',
    '0xed2fe179c18fa528da2392532998560bd1008511'
]
```

## caver.wallet.newKeyring <a href="#caver-wallet-newkeyring" id="caver-wallet-newkeyring"></a>

```javascript
caver.wallet.newKeyring(address, key)
```

주어진 파라미터로 키링 인스턴스를 생성하며 `caver.wallet`에 추가한다.

If `key` is a private key string, a [SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring) instance that uses a single private key is created. If `key` is an array containing private key strings, a [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) instance that use multiple private keys is created. If `key` is a 2D array of which each element contains the private key(s) to be used for each role, a [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring) instance is created. 사용할 키링은 `caver.wallet`에 추가해야 합니다.

**Parameters**

| Name    | Type      | Description |
| ------- | --------- | ----------- |
| address | string    | 주소 문자열입니다.  |
| key     | string \\ | Array       |

**Return Value**

| Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| ------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| object | The keyring instance ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) added to caver.wallet is returned. |

**Example**

```javascript
// Create a instance of SingleKeyring and add to caver.wallet
> caver.wallet.newKeyring('0x{address in hex}', '0x{private key}')
SingleKeyring {
    _address: '0x386a4bb40abbfaa59cecdc3ced202475895fd569',
    _key: PrivateKey { _privateKey: '0x{private key}' }
}

// Create a instance of MultipleKeyring and add to caver.wallet
> caver.wallet.newKeyring('0x{address in hex}', ['0x{private key1}', '0x{private key2}'])
MultipleKeyring {
    _address: '0x17e7531b40ad5d7b5fa7b4ec78df64ce1cb36d24',
    _keys: [ 
        PrivateKey { _privateKey: '0x{private key1}' },
        PrivateKey { _privateKey: '0x{private key2}' }
    ]
}

// Create a instance of RoleBasedKeyring and add to caver.wallet
> const roleBasedKeys = [
    ['0x{private key1}', '0x{private key2}'],
    ['0x{private key3}', '0x{private key4}'],
    ['0x{private key5}', '0x{private key6}'],
]
> caver.wallet.newKeyring('0x{address in hex}', roleBasedKeys)
RoleBasedKeyring {
    _address: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _keys: [
        [
            PrivateKey { _privateKey: '0x{private key1}' },
            PrivateKey { _privateKey: '0x{private key2}' }
        ],
        [ 
            PrivateKey { _privateKey: '0x{private key3}' },
            PrivateKey { _privateKey: '0x{private key4}' }
        ],
        [ 
            PrivateKey { _privateKey: '0x{private key5}' },
            PrivateKey { _privateKey: '0x{private key6}' }
        ]
    ]
}
```

## caver.wallet.updateKeyring <a href="#caver-wallet-updatekeyring" id="caver-wallet-updatekeyring"></a>

```javascript
caver.wallet.updateKeyring(keyring)
```

`caver.wallet` 안에 있는 키링을 업데이트합니다. When a new `keyring` instance ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) is passed as a parameter, the existing keyring stored in the `caver.wallet` that matches the `address` property of the given `keyring` instance is found and replaced with the given one. 일치하는 키링을 찾을 수 없는 경우 에러가 발생합니다.

**Parameters**

| Name    | Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| ------- | ------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| keyring | object | The new keyring ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) to be stored in `caver.wallet`. |

**Return Value**

| Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| object | The updated keyring ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) stored in `caver.wallet`. |

**Example**

```javascript
> caver.wallet.updateKeyring(newKeyring)
SingleKeyring {
    _address: '0x386a4bb40abbfaa59cecdc3ced202475895fd569',
    _key: PrivateKey { _privateKey: '0x{private key}' }
}
```

## caver.wallet.getKeyring <a href="#caver-wallet-getkeyring" id="caver-wallet-getkeyring"></a>

```javascript
caver.wallet.getKeyring(address)
```

`caver.wallet` 주소에 일치하는 키링 인스턴스를 반환합니다.

**Parameters**

| Name    | Type   | Description    |
| ------- | ------ | -------------- |
| address | string | 조회할 키링의 주소입니다. |

**Return Value**

| Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| ------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| object | The found keyring instance ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) stored in `caver.wallet`. |

**Example**

```javascript
> caver.wallet.getKeyring('0x386a4bb40abbfaa59cecdc3ced202475895fd569')
SingleKeyring {
    _address: '0x386a4bb40abbfaa59cecdc3ced202475895fd569',
    _key: PrivateKey { _privateKey: '0x{private key}' }
}
```

## caver.wallet.isExisted <a href="#caver-wallet-isexisted" id="caver-wallet-isexisted"></a>

```javascript
caver.wallet.isExisted(address)
```

Returns `true` if there is a keyring matching the address.

**Parameters**

| Name    | Type   | Description                                |
| ------- | ------ | ------------------------------------------ |
| address | string | The address of keyring to check existence. |

**Return Value**

| Type    | Description                                                                        |
| ------- | ---------------------------------------------------------------------------------- |
| boolean | `true` means a keyring matching with the address is existed in the `caver.wallet`. |

**Example**

```javascript
> caver.wallet.isExisted('0x386a4bb40abbfaa59cecdc3ced202475895fd569')
true
```

## caver.wallet.add <a href="#caver-wallet-add" id="caver-wallet-add"></a>

```javascript
caver.wallet.add(keyring)
```

Adds an instance of keyring to the `caver.wallet`. If the newly given keyring has the same address with one of the keyrings that already exist in `caver.wallet`, an error is returned. In this case, use [updateKeyring](#caver-wallet-updatekeyring) to update the existing keyring in `caver.wallet`.

**Parameters**

| Name    | Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                |
| ------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| keyring | object | A keyring instance ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) to add to `caver.wallet`. |

**Return Value**

| Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                        |
| ------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| object | The added keyring ([SingleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#singlekeyring), [MultipleKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#multiplekeyring) or [RoleBasedKeyring](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#rolebasedkeyring)) in `caver.wallet`. |

**Example**

```javascript
> caver.wallet.add(keyring)
SingleKeyring {
    _address: '0x386a4bb40abbfaa59cecdc3ced202475895fd569',
    _key: PrivateKey { _privateKey: '0x{private key}' }
}
```

## caver.wallet.remove <a href="#caver-wallet-remove" id="caver-wallet-remove"></a>

```javascript
caver.wallet.remove(address)
```

Deletes the keyring from `caver.wallet` whose address matches the address of the given keyring.

**Parameters**

| Name    | Type   | Description                                                |
| ------- | ------ | ---------------------------------------------------------- |
| address | string | An address of the keyring to be deleted in `caver.wallet`. |

**Return Value**

| Type    | Description                                       |
| ------- | ------------------------------------------------- |
| boolean | `true` if keyring is removed from `caver.wallet`. |

**Example**

```javascript
> caver.wallet.remove('0x6a3edfad6d1126020d5369e9097db39281876c5d')
true
```

## caver.wallet.signMessage <a href="#caver-wallet-signmessage" id="caver-wallet-signmessage"></a>

```javascript
caver.wallet.signMessage(address, message, role [, index])
```

Signs the message with Klaytn-specific prefix using keyring stored in caver.wallet. 다음 메서드는 Klaytn 고유의 서명을 계산합니다.

```
sign(keccak256("\x19Klaytn Signed Message:\n" + len(message) + message)))
```

If the user has not provided the index parameter, `caver.wallet.signMessage` signs message using all the private keys used by the role. If the index parameter is given, `caver.wallet.signMessage` signs message using only one private key at the given index. The role used in caver-js can be found from `caver.wallet.keyring.role`.

**Parameters**

| Name    | Type   | Description                                                                                                                                                                                                                    |
| ------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| address | string | 사용될 키링의 주소입니다.                                                                                                                                                                                                                 |
| message | string | 서명할 메시지입니다.                                                                                                                                                                                                                    |
| role    | number | 키의 역할을 나타내는 숫자입니다. `caver.wallet.keyring.role`를 사용할 수 있습니다.                                                                                                                                                                    |
| index   | number | (optional) The index of the private key you want to use. The index must be less than the length of the array of the private keys defined for each role. If an index is not defined, this method will use all the private keys. |

**Return Value**

| Type   | Description        |
| ------ | ------------------ |
| object | 서명 결과를 포함하는 객체입니다. |

반환된 객체는 다음을 포함합니다.

| Name        | Type   | Description                                                                                                                            |
| ----------- | ------ | -------------------------------------------------------------------------------------------------------------------------------------- |
| messageHash | string | Klaytn 고유의 접두사를 가진 메시지의 해시입니다.                                                                                                         |
| signatures  | Array  | An array of [SignatureData](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/keyring#signaturedata). |
| message     | string | The message to sign.                                                                                                                   |

**Example**

```javascript
// Sign message with roleTransactionKey which uses two private keys
> caver.wallet.signMessage('0x386a4bb40abbfaa59cecdc3ced202475895fd569', 'message to sign', caver.wallet.keyring.role.roleTransactionKey)
{
    messageHash: '0x9c4c1ae0aa1faf7e59eaf6fcf36a34542698197b379a9949b58c92925e74c069',
    signatures: [
        SignatureData { _v: '0x1c', _r: '0xb3239...', _s: '0x584d2...' },
        SignatureData { _v: '0x1b', _r: '0x13c64...', _s: '0x60c61...' }
    ],
    message: 'message to sign'
}

// Sign message with roleTransactionKey and index
> caver.wallet.signMessage('0x386a4bb40abbfaa59cecdc3ced202475895fd569', 'message to sign', caver.wallet.keyring.role.roleTransactionKey, 1)
{
    messageHash: '0x9c4c1ae0aa1faf7e59eaf6fcf36a34542698197b379a9949b58c92925e74c069',
    signatures: [
        SignatureData { _v: '0x1b', _r: '0x13c64...', _s: '0x60c61...' }
    ],
    message: 'message to sign'
}
```

## caver.wallet.sign <a href="#caver-wallet-sign" id="caver-wallet-sign"></a>

```javascript
caver.wallet.sign(address, transaction [, index] [, hasher])
```

Signs the transaction as a `sender` of the transaction and appends `signatures` in the transaction object using the keyring in `caver.wallet`.

For [Account Update](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/caver.transaction/basic#accountupdate) transaction, use [roleTransactionKey](https://archive-ko.docs.klaytn.foundation/klaytn/design/accounts#roles), otherwise, use [roleTransactionKey](https://archive-ko.docs.klaytn.foundation/klaytn/design/accounts#roles). If the user has not defined an `index`, `caver.wallet.sign` signs the transaction using all the private keys used by the role. If `index` is defined, the `caver.wallet.sign` signs the transaction using only one private key at the given index.

**Parameters**

| Name        | Type     | Description                                                                                                                                                                                                                                                                                                                                                                                   |
| ----------- | -------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| address     | string   | An address of the keyring to be used.                                                                                                                                                                                                                                                                                                                                                         |
| transaction | object   | An instance of [Transaction](https://github.com/klaytn/klaytn-docs-ko/blob/main/docs/dapp/sdk/caver-js/api-references/caver.transaction#class).                                                                                                                                                                                                                                               |
| index       | number   | (optional) The index of the private key you want to use. The index must be less than the length of the array of the private keys defined for each role. If an index is not defined, this method will use all the private keys.                                                                                                                                                                |
| hasher      | function | (optional) A hash function to get the transaction hash. If `hasher` is given as a parameter, it calculates the transaction hash instead of the default method for calculating transaction hash implemented in caver-js. See [Basic](https://archive-ko.docs.klaytn.foundation/content/klaytn/design/transactions/basic) for details about the default method for transaction hash generation. |

**Return Value**

`Promise` returning `object`: The signed transaction.

| Type   | Description                                                            |
| ------ | ---------------------------------------------------------------------- |
| object | 서명된 트랜잭션 데이터입니다. The sign(s) is added to the `transaction.signatures`. |

For more information about fields by transaction type, see [caver.transaction](https://github.com/klaytn/klaytn-docs-ko/blob/main/docs/dapp/sdk/caver-js/api-references/caver.transaction).

**Example**

```javascript
// This example uses the ValueTransfer transaction.
// Please refer to [caver.transaction] for how to use various transaction types.
> const transaction = caver.transaction.valueTransfer.create({
    from: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    value: 1,
    gas: 30000,
})

> const customHasher = () => { ... }

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleTransactionKey
> caver.wallet.sign('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction).then(console.log)
ValueTransfer {
    _type: 'TxTypeValueTransfer',
    _from: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _gas: '0x7530',
    _signatures: [
        SignatureData { _v: '0x4e43', _r: '0xd78a2...', _s: '0x379e9...' },
        SignatureData { _v: '0x4e43', _r: '0x70a58...', _s: '0x2ab28...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleTransactionKey and index
> caver.wallet.sign('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction, 1).then(console.log)
ValueTransfer {
    _type: 'TxTypeValueTransfer',
    _from: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _gas: '0x7530',
    _signatures: [
        SignatureData { _v: '0x4e43', _r: '0x70a58...', _s: '0x2ab28...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleTransactionKey and hasher
> caver.wallet.sign('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction, customHasher).then(console.log)
ValueTransfer {
    _type: 'TxTypeValueTransfer',
    _from: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _gas: '0x7530',
    _signatures: [
        SignatureData { _v: '0x4e44', _r: '0x7a8b6...', _s: '0x17139...' },
        SignatureData { _v: '0x4e43', _r: '0x7f978...', _s: '0x1a532...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleTransactionKey, index and hasher
> caver.wallet.sign('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction, 0, customHasher).then(console.log)
ValueTransfer {
    _type: 'TxTypeValueTransfer',
    _from: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _gas: '0x7530',
    _signatures: [
        SignatureData { _v: '0x4e44', _r: '0x7a8b6...', _s: '0x17139...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}
```

## caver.wallet.signAsFeePayer <a href="#caver-wallet-signasfeepayer" id="caver-wallet-signasfeepayer"></a>

```javascript
caver.wallet.signAsFeePayer(address, transaction [, index] [, hasher])
```

Signs the transaction as `fee payer` of the transaction and appends `feePayerSignatures` in the transaction object using the keyring in `caver.wallet`.

For signing a transaction as a fee payer, use [roleFeePayerKey](https://archive-ko.docs.klaytn.foundation/klaytn/design/accounts#roles). If the user has not defined an `index`, `caver.wallet.signAsFeePayer` signs the transaction using all the private keys used by the role. If `index` is defined, the `caver.wallet.signAsFeePayer` signs the transaction using only one private key at the given index.

If the `transaction.feePayer` is not defined, the address of keyring which is founded from `caver.wallet` is assigned.

**Parameters**

| Name        | Type     | Description                                                                                                                                                                                                                    |
| ----------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| address     | string   | An address of the keyring to be used.                                                                                                                                                                                          |
| transaction | object   | An instance of [FeeDelegatedTransaction](https://archive-ko.docs.klaytn.foundation/content/dapp/sdk/caver-js/api-references/caver.transaction/fee-delegation).                                                                 |
| index       | number   | (optional) The index of the private key you want to use. The index must be less than the length of the array of the private keys defined for each role. If an index is not defined, this method will use all the private keys. |
| hasher      | function | (optional) A function to get the transaction hash. If hasher is defined as a parameter, this is used to get the transaction hash instead of a default implementation in caver-js.                                              |

**Return Value**

`Promise` returning `object`: The signed transaction.

| Type   | Description                                                                                            |
| ------ | ------------------------------------------------------------------------------------------------------ |
| object | A signed transaction instance. The signing result is appended to the `transaction.feePayerSignatures`. |

For more information about fields by transaction type, see [caver.transaction](https://github.com/klaytn/klaytn-docs-ko/blob/main/docs/dapp/sdk/caver-js/api-references/caver.transaction).

**Example**

```javascript
// This example uses the FeeDelegatedValueTransfer transaction.
// Please refer to [caver.transaction] for how to use various transaction types.
> const transaction = caver.transaction.feeDelegatedValueTransfer.create({
    from: '0x6fddbcb99d31b8755c2b840a367f53eea4b4f45c',
    to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    value: 1,
    gas: 30000,
})

> const customHasher = () => { ... }

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleFeePayerKey
> caver.wallet.signAsFeePayer('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction).then(console.log)
FeeDelegatedValueTransfer {
    _type: 'TxTypeFeeDelegatedValueTransfer',
    _from: '0x6fddbcb99d31b8755c2b840a367f53eea4b4f45c',
    _gas: '0x7530',
    _signatures: [ SignatureData { _v: '0x01', _r: '0x', _s: '0x' } ],
    _feePayer: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _feePayerSignatures: [
        SignatureData { _v: '0x4e44', _r: '0x7010e...', _s: '0x65d6b...' },
        SignatureData { _v: '0x4e43', _r: '0x96ef2...', _s: '0x77f34...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleFeePayerKey, index
> caver.wallet.signAsFeePayer('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction, 0).then(console.log)
FeeDelegatedValueTransfer {
    _type: 'TxTypeFeeDelegatedValueTransfer',
    _from: '0x6fddbcb99d31b8755c2b840a367f53eea4b4f45c',
    _gas: '0x7530',
    _signatures: [ SignatureData { _v: '0x01', _r: '0x', _s: '0x' } ],
    _feePayer: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _feePayerSignatures: [
        SignatureData { _v: '0x4e44', _r: '0x7010e...', _s: '0x65d6b...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleFeePayerKey and hasher
> caver.wallet.signAsFeePayer('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction, customHasher).then(console.log)
FeeDelegatedValueTransfer {
    _type: 'TxTypeFeeDelegatedValueTransfer',
    _from: '0x6fddbcb99d31b8755c2b840a367f53eea4b4f45c',
    _gas: '0x7530',
    _signatures: [ SignatureData { _v: '0x01', _r: '0x', _s: '0x' } ],
    _feePayer: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _feePayerSignatures: [
        SignatureData { _v: '0x4e43', _r: '0xe48bf...', _s: '0x1cf36...' },
        SignatureData { _v: '0x4e43', _r: '0x82976...', _s: '0x3c5e0...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}

// Sign a transaction with the address of RoleBasedKeyring which use two private keys for roleFeePayerKey, index and hasher
> caver.wallet.signAsFeePayer('0xe7e9184c125020af5d34eab7848bab799a1dcba9', transaction, 0, customHasher).then(console.log)
FeeDelegatedValueTransfer {
    _type: 'TxTypeFeeDelegatedValueTransfer',
    _from: '0x6fddbcb99d31b8755c2b840a367f53eea4b4f45c',
    _gas: '0x7530',
    _signatures: [ SignatureData { _v: '0x01', _r: '0x', _s: '0x' } ],
    _feePayer: '0xe7e9184c125020af5d34eab7848bab799a1dcba9',
    _feePayerSignatures: [
        SignatureData { _v: '0x4e43', _r: '0x82976...', _s: '0x3c5e0...' }
    ],
    _to: '0x3424b91026bdc5ec55df4548e6ebf0f28b60abd7',
    _value: '0x1',
    _chainId: '0x2710',
    _gasPrice: '0x5d21dba00',
    _nonce: '0x0'
}
```