Geth JavaScript Console Guide
Use this guide to learn how to set up and use the Geth JS console with an Evmos node.
Go-ethereum responds to instructions encoded as JSON objects as defined in the JSON-RPC-API. To perform and test these instructions, developers can use tools like curl. However, this is a low level and rather error-prone way to interact with the node. Most developers prefer to use convenient libraries that abstract away some of the more tedious and awkward tasks such as converting values from hexadecimal strings into numbers, or converting between denominations of ether (Wei, Gwei, etc). One such library is Web3.js. The purpose of Geth’s Javascript console is to provide a built-in environment to use a subset of the Web3.js libraries to interact with a Geth node. You can use this powerful tool to interact with an Evmos node too!
Prerequisite readings
Installing Go-Ethereum
Install the Go-ethereum CLI (geth) following the procedure corresponding to your OS in the geth docs. This will include the Javascript console.
Check that the installation was successful by running the following command:
geth version
If everything went as expected, you should have an output similar to this:
Geth
Version: 1.10.26-stable
Git Commit: e5eb32acee19cc9fca6a03b10283b7484246b15a
Architecture: amd64
Go Version: go1.18.5
Operating System: linux
GOPATH=/home/tom/go
GOROOT=/usr/local/go
Install dependencies
Make sure you have installed all the dependencies mentioned in the Prerequisite Readings section.
Run Evmos local node
- Clone the evmos repository (if you haven’t already)
- Run the
local_node.shscript to start a local node
git clone https://github.com/evmos/evmos.git
cd evmos
./local_node.sh
Attach geth JS console
Wait a few seconds for the node to start up the JSON-RPC server. The local node has the HTTP-RPC server enabled and is listening at port 8545 by default. Attach a geth console to your node with the following command:
$ geth attach http://127.0.0.1:8545
Welcome to the Geth JavaScript console!
instance: Version dev ()
Compiled at using Go go1.19.2 (amd64)
coinbase: 0x7771fD5e52cf6A81B49d7EF40Bfc2bd0eA8A92E6
at block: 975 (Fri Nov 25 2022 01:21:52 GMT-0300 (-03))
modules: debug:1.0 eth:1.0 net:1.0 personal:1.0 rpc:1.0 txpool:1.0 web3:1.0
To exit, press ctrl-d or type exit
>
Use JSON-RPC methods
Now we can use all implemented JSON-RPC methods. Find an exhaustive list of the supported JSON-RPC methods on Evmos docs.
Below are some examples of how to use the console.
Check current block height
We can check the current block height of the chain:
> eth.blockNumber
1003
> eth.blockNumber
1004
Get accounts
Get an array of the existing accounts in the keyring. To do so, use the following method:
> eth.accounts
["0xf0c3878dd8de6edc0702c06c2bb9a8e380397173", "0xfdd268dfeca95cff23ba385dec161defea031682", "0x35ab07f08f9af9166e9225b3407ad5e63756a084", "0x6a36c1efef7dd58981b3999217cdb3ae720cf330"]
Get chain id
We can get the chain id using:
> net.version
"9000"
Check balances
Check any account balance using the eth.getBalance method:
> eth.getBalance(eth.accounts[0])
9.9999e+25
We get a big number because the result is denominated in aevmos. We can convert to Evmos (10 ^18 aevmos) using the web3.fromWei method:
> web3.fromWei(eth.getBalance(eth.accounts[0]),"ether")
99999000
Send transactions
We can perform token transfers using the corresponding method. For example, let's transfer 1 Evmos token from our account to another account:
> eth.sendTransaction({from:eth.accounts[0], to: eth.accounts[1], value: web3.toWei(1, "ether")})
"0x902dfba22a8b7aaa599aa3ea35c8d60991f497ba2fe6c519ad7a7e1e4a2f3e8f"
As a response, we get back the transaction hash.
Now we can check the balance of the sender and receiver accounts.
The sender balance is reduced by 1 Evmos token and the fees paid for the transaction:
> web3.fromWei(eth.getBalance(eth.accounts[0]),"ether")
99998998.999990548370552
The receiver account balance initially was 100000000 Evmos tokens. After the transaction, the account balance has increased by 1 Evmos token.
> web3.fromWei(eth.getBalance(eth.accounts[1]),"ether")
100000001
🚪 Exit geth console
To exit the geth console use:
> exit
or type Ctrl + D.
🪄 Tips & tricks
List commands
A small trick to see the list of initial commands. Type 2 spaces then hit TAB twice. You will get:
>
AggregateError Function Object TypeError _consoleWeb3Transport encodeURIComponent loadScript toLocaleString
Array GoError Promise URIError _setInterval escape message toString
ArrayBuffer Infinity Proxy Uint16Array _setTimeout eth net txpool
BigNumber Int16Array RangeError Uint32Array clearInterval eval parseFloat undefined
Boolean Int32Array ReferenceError Uint8Array clearTimeout globalThis parseInt unescape
DataView Int8Array Reflect Uint8ClampedArray console hasOwnProperty personal valueOf
Date JSON RegExp WeakMap constructor inspect propertyIsEnumerable web3
Error Map Set WeakSet debug isFinite require
EvalError Math String Web3 decodeURI isNaN rpc
Float32Array NaN Symbol XMLHttpRequest decodeURIComponent isPrototypeOf setInterval
Float64Array Number SyntaxError __proto__ encodeURI jeth setTimeout
The same applies to the different namespaces. For example, you can type eth. and hit TAB twice. You will get:
> eth.
eth._requestManager eth.fillTransaction eth.getGasPrice eth.getTransaction eth.protocolVersion
eth.accounts eth.filter eth.getHashrate eth.getTransactionCount eth.resend
eth.blockNumber eth.gasPrice eth.getHeaderByHash eth.getTransactionFromBlock eth.sendIBANTransaction
eth.call eth.getAccounts eth.getHeaderByNumber eth.getTransactionReceipt eth.sendRawTransaction
eth.chainId eth.getBalance eth.getLogs eth.getUncle eth.sendTransaction
eth.coinbase eth.getBlock eth.getMaxPriorityFeePerGas eth.getWork eth.sign
eth.compile eth.getBlockByHash eth.getMining eth.hashrate eth.signTransaction
eth.constructor eth.getBlockByNumber eth.getPendingTransactions eth.iban eth.submitTransaction
eth.contract eth.getBlockNumber eth.getProof eth.icapNamereg eth.submitWork
eth.createAccessList eth.getBlockTransactionCount eth.getProtocolVersion eth.isSyncing eth.syncing
eth.defaultAccount eth.getBlockUncleCount eth.getRawTransaction eth.maxPriorityFeePerGas
eth.defaultBlock eth.getCode eth.getRawTransactionFromBlock eth.mining
eth.estimateGas eth.getCoinbase eth.getStorageAt eth.namereg
eth.feeHistory eth.getCompilers eth.getSyncing eth.pendingTransactions