Ethereum: Sending Transaction via NodeJS Backend Tutorial

ethereum-backend.js

const web3 = require('web3');
const express = require('express');
const Tx = require('ethereumjs-tx');

const app = express();

//Infura HttpProvider Endpoint
web3js = new web3(new web3.providers.HttpProvider("https://rinkeby.infura.io/YOUR_API_KEY"));

app.get('/sendtx',function(req,res){

        var myAddress = 'ADDRESS_THAT_SENDS_TRANSACTION';
        var privateKey = Buffer.from('YOUR_PRIVATE_KEY', 'hex')
        var toAddress = 'ADRESS_TO_SEND_TRANSACTION';

        //contract abi is the array that you can get from the ethereum wallet or etherscan
        var contractABI =YOUR_CONTRACT_ABI;
        var contractAddress ="YOUR_CONTRACT_ADDRESS";
        //creating contract object
        var contract = new web3js.eth.Contract(contractABI,contractAddress);

        var count;
        // get transaction count, later will used as nonce
        web3js.eth.getTransactionCount(myAddress).then(function(v){
            console.log("Count: "+v);
            count = v;
            var amount = web3js.utils.toHex(1e16);
            //creating raw tranaction
            var rawTransaction = {"from":myAddress, "gasPrice":web3js.utils.toHex(20* 1e9),"gasLimit":web3js.utils.toHex(210000),"to":contractAddress,"value":"0x0","data":contract.methods.transfer(toAddress, amount).encodeABI(),"nonce":web3js.utils.toHex(count)}
            console.log(rawTransaction);
            //creating tranaction via ethereumjs-tx
            var transaction = new Tx(rawTransaction);
            //signing transaction with private key
            transaction.sign(privateKey);
            //sending transacton via web3js module
            web3js.eth.sendSignedTransaction('0x'+transaction.serialize().toString('hex'))
            .on('transactionHash',console.log);
                
            contract.methods.balanceOf(myAddress).call()
            .then(function(balance){console.log(balance)});
        })
    });
app.listen(3000, () => console.log('Example app listening on port 3000!'))

very nice thanks man