The web3.js library is a collection of modules which contain specific functionality for the ethereum ecosystem.

• The web3-eth is for the ethereum blockchain and smart contracts
• The web3-shh is for the whisper protocol to communicate p2p and broadcast
• The web3-bzz is for the swarm protocol, the decentralized file storage
• The web3-utils contains useful helper functions for Dapp developers.

Adding web3.js

First you need to get web3.js into your project. This can be done using the following methods:

• npm: npm install web3
• meteor: meteor add ethereum:web3
• pure js: link the dist/web3.min.js

After that you need to create a web3 instance and set a provider.
Ethereum supported Browsers like Mist or MetaMask will have a ethereumProvider or web3.currentProvider available. For web3.js, check Web3.givenProvider.
If this property is null you should connect to a remote/local node.

… code-block:: javascript

// in node.js use: var Web3 = require('web3');

var web3 = new Web3(Web3.givenProvider || "ws://localhost:8546");

That’s it! now you can use the web3 object.

const Web3 = require('web3');
const Provider = require('@truffle/hdwallet-provider');
const MyContract = require('./build/contracts/MyContract.json');
const address = '';
const privateKey = '';
const infuraUrl = ''; 

//Hard way (web3#signTransaction() + web3#sendSignedTransaction())
const init1 = async () => {
  const web3 = new Web3(infuraUrl);
  const networkId = await web3.eth.net.getId();
  const myContract = new web3.eth.Contract(
    MyContract.abi,
    MyContract.networks[networkId].address
  );

  const tx = myContract.methods.setData(1);
  const gas = await tx.estimateGas({from: address});
  const gasPrice = await web3.eth.getGasPrice();
  const data = tx.encodeABI();
  const nonce = await web3.eth.getTransactionCount(address);

  const signedTx = await web3.eth.accounts.signTransaction(
    {
      to: myContract.options.address, 
      data,
      gas,
      gasPrice,
      nonce, 
      chainId: networkId
    },
    privateKey
  );
  console.log(`Old data value: ${await myContract.methods.data().call()}`);
  const receipt = await web3.eth.sendSignedTransaction(signedTx.rawTransaction);
  console.log(`Transaction hash: ${receipt.transactionHash}`);
  console.log(`New data value: ${await myContract.methods.data().call()}`);
}

//Slightly easier (web3#sendTransaction())
const init2 = async () => {
  const web3 = new Web3(infuraUrl);
  const networkId = await web3.eth.net.getId();
  const myContract = new web3.eth.Contract(
    MyContract.abi,
    MyContract.networks[networkId].address
  );
  web3.eth.accounts.wallet.add(privateKey);

  const tx = myContract.methods.setData(2);
  const gas = await tx.estimateGas({from: address});
  const gasPrice = await web3.eth.getGasPrice();
  const data = tx.encodeABI();
  const nonce = await web3.eth.getTransactionCount(address);
  const txData = {
    from: address,
    to: myContract.options.address,
    data: data,
    gas,
    gasPrice,
    nonce, 
    chain: 'rinkeby', 
    hardfork: 'istanbul'
  };

  console.log(`Old data value: ${await myContract.methods.data().call()}`);
  const receipt = await web3.eth.sendTransaction(txData);
  console.log(`Transaction hash: ${receipt.transactionHash}`);
  console.log(`New data value: ${await myContract.methods.data().call()}`);
}

//Easy way (Web3 + @truffle/hdwallet-provider)
const init3 = async () => {
  const provider = new Provider(privateKey, 'https://rinkeby.infura.io/v3/74aa9a15e2524f6980edb8a377301f3c'); 
  const web3 = new Web3(provider);
  const networkId = await web3.eth.net.getId();
  const myContract = new web3.eth.Contract(
    MyContract.abi,
    MyContract.networks[networkId].address
  );

  console.log(await myContract.methods.data().call());
  console.log(`Old data value: ${await myContract.methods.data().call()}`);
  const receipt = await myContract.methods.setData(3).send({ from: address });
  console.log(`Transaction hash: ${receipt.transactionHash}`);
  console.log(`New data value: ${await myContract.methods.data().call()}`);
}

init3();

Read more docs: https://web3js.readthedocs.io/en/v1.2.1/web3-eth.html#sendtransaction

#node #nodejs #web3 #eth #ethereum