caver-js is a JavaScript API library that allows developers to interact with a Klaytn node using a HTTP or Websocket connection.

• Requirements
• Installation
• Getting Started
  • Check the Connection
  • Using caver-js account/wallet
  • Submitting a Transaction
  • Units for KLAY
• Documentation
• API Specification
• Web3.js Similarity
• Error Code Improvement
• Sample Projects
• Github Repository
• Related Projects

The following packages are required to use the caver-js library.

• Node.js
• npm
• gcc-c++

Testing in caver-js is implemented using the mocha testing framework. If you want to run unit tests in caver-js, you need to install mocha first.

• mocha

Note caver-js can run on Node.js versions 8 and 10, and the recommended versions are:

• lts/carbon (8.16.0)
• lts/dubnium (10.16.0)

If you are already using a different version of the node(for example, node v12), use the Node Version Manager(NVM) to install and use the version supported by caver-js.

To try it out, install caver-js with npm like following command:

$ npm install caver-js

Note package.json file should exist on the same install path. If it does not exist, package.json should be generated via npm init.

To install a specific version of caver-js, try the following command:

$ npm install [email protected]

If you want to run your own EN (Endpoint Node), see EN Operation Guide to set up. You can also use Klaytn Public EN like below:

$ node
> const Caver = require('caver-js')
> const caver = new Caver('https://api.baobab.klaytn.net:8651/')

Note The above example should be executed from the location where caver-js is installed, and the example is explained using Node.js REPL.

You can now use caver-js. You can send a basic request to the node as shown below and check the results.

> caver.klay.getNodeInfo().then(console.log)
Klaytn/vX.X.X/linux-amd64/goX.X.X

You can easily manage your account by using the account / wallet packages provided by caver-js. caver.klay.accounts package provides functions related to accounts, such as create, signTransaction, and privateKeyToAccount. caver.klay.accounts.wallet provides the in-memory wallet for easy account management in caver-js.

Note Functions associated with wallet and account provided by caver-js have no effect on the actual Klaytn network.

Let's create a random account as shown in the example below:

> const account = caver.klay.accounts.create()

> account
{ address: '0xF5b66670135666F273F6b5a2eA706A5aCf38D8D5',
  privateKey: '0x{private key}',
  ... }

You can add to the wallet instance of caver-js using the account object created in the above example, or you can add an account using a specific private key. If the address is not specified separately, the address derived from the private key is set. If the private key is decoupled from the address, pass the address as a second parameter separately shown below.

// Adding an account object
> caver.klay.accounts.wallet.add(account)

// Adding a private key
> caver.klay.accounts.wallet.add('0x{private key}')

// Adding a private key with an address
> caver.klay.accounts.wallet.add('0x{private key}', '0x6b6bb1221c5c27cbc87768aae849b97d01a073a9')

caver-js supports two types of private key formats. One is a raw private key format of a 32-byte string type and the other is the KlaytnWalletKey.

You can also add your account using the KlaytnWalletKey format as shown below:

// Adding a Klaytn wallet key
> caver.klay.accounts.wallet.add('0x{private key}0x000x{address in hex}')

Once added to a wallet, it can be accessed via an index or an address.

> caver.klay.accounts.wallet[0]
> caver.klay.accounts.wallet['0xF5b66670135666F273F6b5a2eA706A5aCf38D8D5']

The private key that matches a specific account stored in the wallet instance can be updated as follows:

> caver.klay.accounts.wallet.updatePrivateKey('0x{new private key}', '0x{address in hex}')

You can use caver-js to submit various types of transactions to a node. Please refer to the caver.klay.sendTransaction to see how to send a transaction of each type.

You can submit the transaction as shown below, and the result can be confirmed by the returned receipt:

// using the promise
> caver.klay.sendTransaction({
    type: 'VALUE_TRANSFER',
    from: '0x76d1cc1cdb081de8627cab2c074f02ebc7bce0d0',
    to: '0x80c2c57dad6cb16488b4c70c17d77152c74f8ade',
    gas: '300000',
    value: caver.utils.toPeb('1', 'KLAY'),
  }).then(console.log)
{ 
  blockHash: '0x0a78b5c5b95456b2d6b6a9ba25fd2afd0000d16bcf03a8ae58a6557a59319a67',
  blockNumber: 8021,
  contractAddress: null,
  from: '0x76d1cc1cdb081de8627cab2c074f02ebc7bce0d0',
  ...
  type: 'TxTypeValueTransfer',
  typeInt: 8,
  value: '0xde0b6b3a7640000' 
}

// using the event emitter
> caver.klay.sendTransaction({
    type: 'VALUE_TRANSFER',
    from: '0x76d1cc1cdb081de8627cab2c074f02ebc7bce0d0',
    to: '0x80c2c57dad6cb16488b4c70c17d77152c74f8ade',
    gas: '300000',
    value: caver.utils.toPeb('1', 'KLAY'),
  }).on('transactionHash', function(hash){
    ...
  }).on('receipt', function(receipt){
    ...
  })

The sendTransaction function will sign if the account corresponding to from is in the wallet and send it to the node; otherwise, send the transaction unsigned.

If you want to get a raw signed transaction, do the following with an appropriate private key:

> caver.klay.accounts.signTransaction({
    type: 'VALUE_TRANSFER',
    from: '0x76d1cc1cdb081de8627cab2c074f02ebc7bce0d0',
    to: '0x80c2c57dad6cb16488b4c70c17d77152c74f8ade',
    gas: '300000',
    value: caver.utils.toPeb('1', 'KLAY'),
  }, '{private key}').then((signed)=>console.log(signed.rawTransaction))

The raw transaction can be transferred to the Klaytn node using caver.klay.sendSignedTransaction:

> caver.klay.sendSignedTransaction(rawTransaction).then(console.log)

Units of KLAY is shown as below, and peb is the smallest currency unit. peb is the default unit unless the unit conversion is used.

caver-js provides the caver.utils.toPeb function for unit conversion. Please refer to the usage below.

> caver.utils.toPeb(1, 'peb')
'1'

> caver.utils.toPeb(1, 'Gpeb')
'1000000000'

> caver.utils.toPeb(1, 'KLAY')
'1000000000000000000'

Documentation can be found at Klaytn Docs-caver-js.

The API lists of caver-js are described in folloinwg links:

• caver.klay
• caver.klay.accounts
• caver.klay.contract
• caver.klay.net
• caver.klay.abi
• caver.utils

Since caver-js has been evolved from web3.js, usage pattern of caver-js is very similar to that of web3.js. This means a software developed using web3.js can be easily converted to caver-js. The following examples are code patterns used in web3.js and caver-js, respectively.

const Web3 = require('web3');
const web3 = new Web3(new web3.providers.HttpProvider('http://localhost:8545'));

web3.eth.getBalance('0x407d73d8a49eeb85d32cf465507dd71d507100c1').then(console.log)

const Caver = require('caver-js');
const caver = new Caver(new Caver.providers.HttpProvider('http://localhost:8545'));

caver.klay.getBalance('0x407d73d8a49eeb85d32cf465507dd71d507100c1').then(console.log)

Klaytn improves reporting transaction failure via txError in the receipt. caver-js further improves the report by presenting the error string that corresponds to txError.

The below is an example of a receipt containing txError.

Error: VM error occurs while running smart contract
 {
  "blockHash": "0xe7ec35c9fff1178d52cee1d46d40627d19f828c4b06ad1a5c3807698b99acb20",
  ...
  "txError": "0x2",
  ...
}

The meaning of error code can be found below:

The BApp (Blockchain Application) Development sample projects using caver-js are the following:

• Count BApp
• Klaystagram

• caver-js

caver-java for Java