Error Handling

Use try-catch to get RPC error

You can use js-conflux-sdk with async/await syntax, which means you can use try-catch to catch the error. Normally errors returned from RPC server will include code and message field, and optionally data field will also been returned.

try {
} catch(e) {

The data field is a plain text string, or is a hex encoded string.

// You should connect a node with version 1.1.1 or pass a valid hex value
// 0x5265766572746564
// For hex string you can use hex decode to convert it to plain string
// For example in node.js you can decode like this
Buffer.from(, 'hex').toString()

From SDK V2.0 the hex encoded, will be auto decoded by SDK, you can catch and check it through

Common Errors

Method not found

Method not found means you send a RPC request, and the request's method is not supported by the fullnode RPC service. If you are invoke cfx.sendTransaction() and seen this error, normally because cfx.wallet doesn't have the account tx.from, you should add it to wallet through cfx.addPrivateKey().

0x prefix is missing

0x prefix is missing means the RPC server expect a hex encoded string, but the request params is not passed correctly.

Notes: If you use js-conflux-sdk version 1.5.10 or above, it will use the new CIP37 format address for RPC request parameters. It only work with conflux node version 1.1.1 or above, if you use newer version SDK with 1.1.0 or below you will seen this error 0x prefix is missing. To resolve it you need use a newer version RPC work with it.

ParserError(argument|input error)

The format utility provide a lot format methods that can convert data from one type to another type. For example format.hex, format.hexBuffer, format.uInt, format.bigInt. These convert methods use the Parser underline, if any convert operation failed it will throw a ParserError. format has been heavy used in SDK, including RPC parameter and response format, contract method parameter format and etc.

So if you see any ParserError which means some invalid value is used.

> format.hex('hello')
Uncaught ParserError: path="", toHex(hello), hello not match "hex"
    at Proxy.parser (/Users/xxxx/Projects/conflux/sdks/js-conflux-sdk/src/util/parser.js:37:13) {
  arguments: [Arguments] { '0': 'hello' },
  path: []
> format.hex(undefined)
Uncaught ParserError: path="", toHex(), undefined not match "hex"
    at Proxy.parser (/Users/xxxx/Projects/conflux/sdks/js-conflux-sdk/src/util/parser.js:37:13) {
  arguments: [Arguments] { '0': undefined },
  path: []

> format.uInt("hello")
Uncaught ParserError: path="", NaN do not match "uint"
    at Proxy.parser (/Users/xxxx/Projects/conflux/sdks/js-conflux-sdk/src/util/parser.js:37:13) {
  arguments: [Arguments] { '0': 'hello' },
  path: []

From SDK V2.0 the parser error will provide more info, include code, Parser's error code is 5200

> format.hex(undefined)
Uncaught ParserError: undefined not match "hex"
    at toHex (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/util/format.js:29:11)
    at ParserContext.<anonymous> (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/util/parser.js:161:14)
    at Proxy.parser (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/util/parser.js:40:17)
    at repl:1:8
    at Script.runInThisContext (vm.js:120:18)
    at REPLServer.defaultEval (repl.js:433:29)
    at bound (domain.js:427:14)
    at REPLServer.runBound [as eval] (domain.js:440:12)
    at REPLServer.onLine (repl.js:760:10)
    at REPLServer.emit (events.js:327:22) {
  message: '(Invalid input|args) formatter: "format.hex"; args: (undefined) ; errorMessage: undefined not match "hex"',
  code: 5200,
  arguments: [Arguments] { '0': undefined },
  path: []

cfx_call Error

If you are interacting with contract, and trying query contract state through cfx_call, then you may encounter error Transaction reverted

(node:1416) UnhandledPromiseRejectionWarning: Error: Transaction reverted
    at (/Users/xxxx/Projects/conflux-fans/pos-pool/contract/node_modules/js-conflux-sdk/src/provider/BaseProvider.js:71:13)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async (/Users/xxxx/Projects/conflux-fans/pos-pool/contract/node_modules/js-conflux-sdk/src/rpc/cfx.js:490:14)
    at async (/Users/xxxx/Projects/conflux-fans/pos-pool/contract/node_modules/js-conflux-sdk/src/contract/method/MethodTransaction.js:53:17)
    at async MethodTransaction.then (/Users/xxxx/Projects/conflux-fans/pos-pool/contract/node_modules/js-conflux-sdk/src/contract/method/MethodTransaction.js:74:22)
(node:1416) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see (rejection id: 1)
(node:1416) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Normally this mean contract method call failed, may have a lot reasons, may be parameter passed wrong, maybe do not have permission.

For these situations, you need to find out why contract method execute failed. If you are lucky, contract have provide some error message you can seen it in error message

(node:1416) UnhandledPromiseRejectionWarning: Error: Transaction reverted balance not enough

abi encode error

When interact with contract's method, if provide wrong number of arguments, you will encounter errors like below:

Error: {"message":"length not match","expect":2,"got":1,"coder":{"type":"(address,uint256)","dynamic":false,"size":2,"coders":[{"type":"address","name":"_to","dynamic":false,"networkId":1},{"type":"uint256","name":"_value","dynamic":false,"signed":false,"size":32,"bound":"115792089237316195423570985008687907853269984665640564039457584007913129639936"}],"names":["_to","_value"]}}
    at assert (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/util/index.js:9:11)
    at TupleCoder.encode (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/contract/abi/TupleCoder.js:116:5)
    at ContractMethod.encodeData (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/contract/method/FunctionCoder.js:50:44)
    at (/Users/panaw/Projects/conflux/sdks/js-conflux-sdk/src/contract/method/ContractMethod.js:16:23)
    at invokeContractMethod (/Users/panaw/Projects/conflux/sdks/test-jssdk/main/v2/traceV2.js:44:31)
    at main (/Users/panaw/Projects/conflux/sdks/test-jssdk/main/v2/traceV2.js:10:9)
    at Object.<anonymous> (/Users/panaw/Projects/conflux/sdks/test-jssdk/main/v2/traceV2.js:16:1)
    at Module._compile (internal/modules/cjs/loader.js:1137:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)
    at Module.load (internal/modules/cjs/loader.js:985:32)

"length not match","expect":2,"got":1 means the abi encoder expect 2 arguments according to the ABI, but only 1 is provided.

notifications not supported

If you use event subscribe methods, a websocket RPC endpoint is required.

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