Web3 examples for ecrecover

sign.js

const Web3 = require('web3')
var utils = require('ethereumjs-util');

const provider = new Web3.providers.HttpProvider('http://localhost:8545')
const web3 = new Web3(provider)

const dorecover = async function(){
    // Recover using account from ganache-cli
    var accounts = await web3.eth.getAccounts()
    let msg = 'I shill your promotion'
    let sig = await web3.eth.sign(msg, accounts[0])
    console.log('  account: ' + accounts[0])
    console.log('      msg: ' + msg) 
    console.log('      sig: ' + sig)
    console.log('recovered: ' + web3.eth.accounts.recover(msg, sig))

    let r = `${sig.slice(0,66)}`
    let s = `0x${sig.slice(66,130)}`
    let v = `0x${sig.slice(130, 132)}`
    console.log('         r: ' + r)
    console.log('         s: ' + s)
    console.log('         v: ' + v)
    console.log('recovered: ' + web3.eth.accounts.recover(msg, v, r, s))

    // Recover using account created from existing private key
    console.log('\n==== account ====== ')
    let privatekey = '0x348ce564d427a3311b6536bbcff9390d69395b06ed6c486954e971d960fe8709'
    let account = web3.eth.accounts.privateKeyToAccount(privatekey)
    console.log(account)
    let sigobj = await web3.eth.accounts.sign(msg, privatekey)
    console.log('sigobj: ', sigobj)
    sig = sigobj.signature
    r = `${sig.slice(0,66)}`
    s = `0x${sig.slice(66,130)}`
    v = `0x${sig.slice(130, 132)}`
    console.log('   address: ' + account.address)
    console.log('       sig: ' + sig)
    console.log('         r: ' + r)
    console.log('         s: ' + s)
    console.log('         v: ' + v)
    console.log(' recovered: ' + web3.eth.accounts.recover(msg, v, r, s))
    console.log(' recovered: ' + web3.eth.accounts.recover(sigobj))
}
dorecover()