Craft Extrinsic

In the current version, crafting an extrinsic is a rather cumbersome process. This sample guides you though it and shows how to tranfer DOTs from an account to another.

const Api = require('@polkadot/api').default
const WsProvider = require('@polkadot/api-provider/ws').default
const extrinsics = require('@polkadot/extrinsics').default
const encodeExtrinsic = require('@polkadot/extrinsics/codec/encode').default
const encodeLength = require('@polkadot/extrinsics/codec/encode/length').default
const Keyring = require('@polkadot/util-keyring').default
const storage = require('@polkadot/storage').default
const BN = require('bn.js')

const Encoder = new TextEncoder()
const keyring = new Keyring()
const provider = new WsProvider('ws://127.0.0.1:9944')
const api = new Api(provider)

async function getAccountIndex (address) {
  return api.state.getStorage([storage.system.public.accountIndexOf, address])
}

async function transfer (keyRingFrom, addressTo, amount) {
  const accountIndex = await getAccountIndex(keyRingFrom.address())

  console.log(`Current accountIndex: ${accountIndex}`)

  // encode the call for signing
  const message = encodeExtrinsic(
    keyRingFrom.publicKey(),
    accountIndex,
    extrinsics.staking.public.transfer,
    [addressTo, amount]
  )

  // get the signature
  const signature = keyRingFrom.sign(message)

  // encode the extrinsic for submission, adding the length (prefix) and the
  // signature (postfix)Rödl
  const encoded = encodeLength(
    // When working with publicKeys, the prefix is 0xff for poc-2+
    new Uint8Array([0xff]),
    message,
    signature
  )

  return api.author.submitExtrinsic(encoded)
}

const Alice = keyring.addFromSeed(Encoder.encode('Alice                           '))
const addressBob = '5Gw3s7q4QLkSWwknsiPtjujPv3XM4Trxi5d4PgKMMk3gfGTE'
const amount = new BN(999) // on dev chain, the fee is 1, that makes it a round 1000

console.log(`Crafting and sending an extrinsic for Alice to send Bob ${amount} DOTs`)

transfer(Alice, addressBob, amount)
  .then(() =>
    console.log('Sent')
  )
  .catch((e) =>
    console.log('HINT: Make sure you wait for the storage to update before sending the next extrinsic', e)
  )
  .finally(_ => process.exit(0))