caver-js

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

Table of contents

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

Requirements

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 (8.17.0)
• lts/dubnium (10.22.0)

• lts/erbium (12.19.0)

If you are already using a different version of the node(for example, node v14), use the Node Version Manager(NVM) to install and use the version supported by caver-js.

Installation

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]

Getting Started

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

$ node
> const Caver = require('caver-js')
> const caver = new Caver('http://localhost:8551/')

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

Check the Connection

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

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

Using caver-js keyring/wallet

You can easily use your Klaytn account when signing a transaction or message by using the Keyring / wallet.

The keyring is a new feature that contains an address and one or more private keys based on the key types (SingleKeyring, MultipleKeyring or RoleBasedKeyring). Refer to caver.wallet.keyring for details. caver.wallet, the in-memory wallet, is provided to easily manage multiple keyrings.

Note Functions associated with wallet and keyring have no effect on the Klaytn blockchain platform. It just manipulates keyrings in the in-memory wallet.

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

> const keyring = caver.wallet.keyring.generate()

> keyring
SingleKeyring {
  _address: '0x64d221893cc628605314026f4c4e0879af5b75b1',
  _key: PrivateKey { _privateKey: '0x{private key}' }
}

You can add the keyring object created in the above example to the caver.wallet, or you can add a keyring using an address and private key(s).

// Add a keyring instance to caver.wallet
> caver.wallet.add(keyring)

// Add a keyring to caver.wallet with an address and a private key
> caver.wallet.newKeyring('0x{address in hex}', '0x{private key}')

// Add a keyring to caver.wallet with an address and private keys
> caver.wallet.newKeyring('0x{address in hex}', ['0x{private key1}', '0x{private key2}', ...])

// Add a keyring to caver.wallet with an address and private keys by roles
> caver.wallet.newKeyring('0x{address in hex}', [ ['0x{private key1}', ...], ['0x{private key2}', ...], ['0x{private key3}', ...] ])

Submitting a Transaction

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

You can sign the transaction using a keyring and send a signed transaction through caver.rpc.klay.sendRawTransaction as shown below, and the receipt is returned as a result.

// Add a keyring to caver.wallet
> const keyring = caver.wallet.newKeyring('0x{address in hex}', '0x{private key}')
> const vt = new caver.transaction.valueTransfer({
		from: keyring.address,
		to: '0x176ff0344de49c04be577a3512b6991507647f72',
		value: caver.utils.convertToPeb(1, 'KLAY'),
		gas: 25000,
	})
> caver.wallet.sign(keyring.address, vt).then(signed => {
  caver.rpc.klay.sendRawTransaction(signed).then(console.log)
})
{ 
  blockHash: '0x0a78b5c5b95456b2d6b6a9ba25fd2afd0000d16bcf03a8ae58a6557a59319a67',
  blockNumber: 8021,
  contractAddress: null,
  from: '0x09a08f2289d3eb3499868908f1c84fd9523fe11b',
  ...
  type: 'TxTypeValueTransfer',
  typeInt: 8,
  value: '0xde0b6b3a7640000' 
}

The above example uses Promise when sending a signed transaction to the Klaytn. You can also use event emitter like below.

caver.rpc.klay.sendRawTransaction(signed).on('transactionHash', function(hash){
    ...
  }).on('receipt', function(receipt){
    ...
  })

Units for KLAY

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.convertToPeb function for unit conversion. Please refer to the usage below.

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

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

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

Documentation

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

API Specification

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

• caver.account
• caver.wallet
• caver.wallet.keyring
• caver.transaction
• caver.rpc.klay
• caver.rpc.net
• caver.contract
• caver.abi
• caver.kct.kip7
• caver.kct.kip17
• caver.utils
• caver.ipfs

Web3.js Similarity

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

Error Code Improvement

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:

Sample Projects

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

• Count BApp
• Klaystagram

Github Repository

• caver-js

Related Projects

caver-java for Java