How to make transactions using private key in web3?

Question

I have account private key, contract address and abi and I need to call contract function with this account. Is it possible?

Answer 1

Along with web3 you have to use ethereumjs-tx to sign the transaction and you can send web3.eth.sendRawTransaction to the network. Below code for your reference.

const Web3 = require("web3");
const solc = require("solc");
const Tx = require('ethereumjs-tx')
const web3 = new Web3(new 

Web3.providers.HttpProvider("https://ropsten.infura.io"));

var account = "Your Account #";
var key = new Buffer('Your Account # Private key', 'hex')

var abi = ABI of the Contract
var bytecode = Bytecode of compiled contract
var Contract = web3.eth.contract(abi)

const gasPrice = web3.eth.gasPrice;
const gasPriceHex = web3.toHex(gasPrice);
const gasLimitHex = web3.toHex(3000000);

var tra = {
    gasPrice: gasPriceHex,
    gasLimit: gasLimitHex,
    data: bytecode,
    from: account
};

var tx = new Tx(tra);
tx.sign(key);

var stx = tx.serialize();
web3.eth.sendRawTransaction('0x' + stx.toString('hex'), (err, hash) => {
    if (err) { console.log(err); return; }
    console.log('contract creation tx: ' + hash);
});