Web3.js Basic

Web3.js talks to The Ethereum Blockchain with JSON RPC, which stands for "Remote Procedure Call" protocol. Ethereum is a peer-to-peer network of nodes that stores a copy of all the data and code on the blockchain. Web3.js allows us to make requests to an individual Ethereum node with JSON RPC in order to read and write data to the network. It's kind of like using jQuery with a JSON API to read and write data with a web server.

  

image credit: iotbl. 

Infura is a service that provides a remote Ethereum node for free. All you need to do is sign up and obtain an API key and the RPC URL for the network you want to connect to.

image credit: https://www.youtube.com/watch?v=bcgFG0RoIPU 

Example: Checking Account Balances

Testing address: https://etherscan.io/address/0xf977814e90da44bfa03b6295a0616a897441acec

$ npm install web3

example1.js:

const Web3 = require('web3')

const rpcURL = "https://mainnet.infura.io/v3/YOUR_INFURA_API_KEY"

const web3 = new Web3(rpcURL)

const address = "0xf977814e90da44bfa03b6295a0616a897441acec" // Binance 8

web3.eth.getBalance(address, (err, wei) => {

  balance = web3.utils.fromWei(wei, 'ether')

  console.log(`balance=${balance} ETH`);

})

$ node .\example1.js
balance=2436827.427985396101008923 ETH