publishAndFetchPublic.js

const Mam = require('../lib/mam.client.js')
const { asciiToTrytes, trytesToAscii } = require('@iota/converter')

const mode = 'public'
const provider = 'https://nodes.devnet.iota.org'

const mamExplorerLink = `https://mam-explorer.firebaseapp.com/?provider=${encodeURIComponent(provider)}&mode=${mode}&root=`

// Initialise MAM State
let mamState = Mam.init(provider)

// Publish to tangle
const publish = async packet => {
    // Create MAM Payload - STRING OF TRYTES
    const trytes = asciiToTrytes(JSON.stringify(packet))
    const message = Mam.create(mamState, trytes)

    // Save new mamState
    mamState = message.state

    // Attach the payload
    await Mam.attach(message.payload, message.address, 3, 9)

    console.log('Published', packet, '\n');
    return message.root
}

const publishAll = async () => {
  const root = await publish({
    message: 'Message from Alice',
    timestamp: (new Date()).toLocaleString()
  })

  await publish({
    message: 'Message from Bob',
    timestamp: (new Date()).toLocaleString()
  })

  await publish({
    message: 'Message from Charlie',
    timestamp: (new Date()).toLocaleString()
  })

  return root
}

// Callback used to pass data out of the fetch
const logData = data => console.log('Fetched and parsed', JSON.parse(trytesToAscii(data)), '\n')

publishAll()
  .then(async root => {

    // Output asyncronously using "logData" callback function
    await Mam.fetch(root, mode, null, logData)

    // Output syncronously once fetch is completed
    const result = await Mam.fetch(root, mode)
    result.messages.forEach(message => console.log('Fetched and parsed', JSON.parse(trytesToAscii(message)), '\n'))

    console.log(`Verify with MAM Explorer:\n${mamExplorerLink}${root}\n`);
  })