# caver-js \~v1.4.1

`caver-js` is a JavaScript API library that allows developers to interact with a Klaytn node using a HTTP or Websocket connection. It is available on [npm](https://www.npmjs.com/package/caver-js).

## Features <a href="#features" id="features"></a>

* Complete implementation of Klaytn’s JSON-RPC client API over HTTP and Websocket
* Support of Klaytn transaction, account, and account key types
* JavaScript smart contract package to deploy and execute a smart contract on the Klaytn network
* In-memory wallet for managing Klaytn accounts
* Support of fee-delegation
* Support of the Klaytn wallet key format
* Encoding/decoding of a transaction object in RLP
* Signing of a transaction object
* Easy to port web3-js application to caver-js

## Packages in caver-js <a href="#packages-in-caver-js" id="packages-in-caver-js"></a>

Below are packages provided in `caver-js`.

* [caver.klay](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/v1.4.1/api-references/caver.klay)
* [caver.klay.accounts](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/v1.4.1/api-references/caver.klay.accounts)
* [caver.klay.Contract](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/v1.4.1/api-references/caver.klay.contract)
* [caver.klay.net](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/v1.4.1/api-references/caver.klay.net)
* [caver.klay.abi](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/v1.4.1/api-references/caver.klay.abi)
* [caver.utils](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/v1.4.1/api-references/caver.utils_1.4.1)

## Error Code Improvement <a href="#error-code-improvement" id="error-code-improvement"></a>

The error messages from Ethereum via web3.js are hardly figuring out where the error occurs. `caver-js` improves the interface to catch error messages from Klaytn.

More details can be found in the value of `txError` of the transaction receipt like the below:

```
Error: runtime error occurred in interpreter
 {
  "blockHash": "0xe7ec35c9fff1178d52cee1d46d40627d19f828c4b06ad1a5c3807698b99acb20",
  "blockNumber": 7811,
  "contractAddress": null,
  "from": "0xa8a2d37727197cc0eb827f8c5a3a3aceb26cf59e",
  "gasUsed": 9900000000,
  "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  "status": false,
  "to": "0xf8425b0f65147969621f9390ca06139c7b439497",
  "transactionHash": "0x85ce2b307899c90144442d9b3236827ac57375c522be2435093aebfd920b8c58",
  "transactionIndex": 0,
  "txError": "0x2",
  "events": {}
}
```

## Caution when Sending a Transaction to Klaytn <a href="#caution-when-sending-a-transaction-to-klaytn" id="caution-when-sending-a-transaction-to-klaytn"></a>

Klaytn uses a fixed gas price (25 ston = 25 \* 10^9). If a transaction with other gas price is submitted to the Klaytn network, it is rejected. For more information about the gas price, see [Gas and Unit Price Overview](https://klaytn.gitbook.io/docs/klaytn/design/transaction-fees#gas-and-unit-price-overview) The price of gas used in the network can be obtained by using [caver.klay.getGasPrice](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/api-references/caver.klay/config#getgasprice).

If `gasPrice` is not defined when you sign or submit a transaction, caver-js uses the [caver.klay.getGasPrice](https://klaytn.gitbook.io/docs/bapp/sdk/caver-js/api-references/caver.klay/config#getgasprice) RPC call to set the gas price of the transaction.

## Links <a href="#links" id="links"></a>

* caver-js [GitHub repository](https://github.com/klaytn/caver-js)
* caver-js on [npm](https://www.npmjs.com/package/caver-js)