how to call contract method using sendRawTransaction

Question

const privateKeyStr = "";
const privateKey = new Buffer(privateKeyStr, 'hex');
const contractAddress = '0x';
const COO = '0x';
let contractAddress = '0x';

let myContract = ...;
//some other articles told use getData method , but getData is undefined. so is use request instead.
let payloadData = myContract.contractMethodName.request(methodParams).params[0].data;

let rawTx = {
    nonce:  web3.toHex(web3.eth.getTransactionCount(fromAccount)),
    gas:   web3.toHex("21000"),
    gasPrice: web3.toHex(web3.eth.gasPrice.toNumber()), 
    gasLimit: web3.toHex(40000),
    from:   fromAccount,
    to: contractAddress,
    data:   payloadData
};

var tx = new Tx(rawTx);
tx.sign(privateKey);

var serializedTx = '0x' + tx.serialize().toString('hex');
web3.eth.sendRawTransaction(serializedTx, function(err, hash) {
    if (!err){
        console.log('transaction hash : ',hash);
        process.exit(0);
    } else {
        console.error('error is ',err);
        process.exit(1);
    }
});

Answer 1

Try this way.

var data = myContract.contractMethodName.getData(params, {from: senderAddr});
var gasPrice = 0.8; //var gasPrice = web3.eth.gasPrice;
var gasLimit = 3000000;

var rawTransaction = {
  "from": senderAddr,
  "nonce": web3.toHex(nonce),
  "gasPrice": web3.toHex(gasPrice * 1e9),
  "gasLimit": web3.toHex(gasLimit),
  "to": contractAddress,
  "value": "0x00",
  "data": data,
  "chainId": 4 //change the chainID accordingly
};

var privKey = new Buffer(privateKey, 'hex');
var tx = new Tx(rawTransaction);

tx.sign(privKey);
var serializedTx = tx.serialize();

web3.eth.sendRawTransaction('0x' + serializedTx.toString('hex'), function(err, hash) {
  if (!err)
      {
        console.log('Txn Sent and hash is '+hash);
      }
  else
      {
        console.error(err);
      }
});

Answer 2

Reading the docs you should do this:

let payloadData = web3.sha3("contractMethodName()").substr(0,10);

Or if you have an argument

var argument = '0';
let payloadData = web3.sha3("contractMethodName(uint256)").substr(0,10);
payloadData += web3.sha3(argument).substr(0,32);

Answer 3

On web3js version 1 it's easy:

const data = contract.methods.contractMethodName(...params).encodeABI();

See the documentation here.