index.js

const { SingleNodeClient } = require("@iota/iota.js")
const { createChannel, createMessage, parseMessage, mamAttach, mamFetch, TrytesHelper } = require('@iota/mam.js');
const crypto = require('crypto');
const fs = require('fs');

async function run(asciiMessage) {
    // Setup the details for the channel.
    const mode = 'restricted';
    const sideKey = 'MYKEY';
    let channelState;

    // Try and load the channel state from json file
    try {
        const currentState = fs.readFileSync('./channelState.json');
        if (currentState) {
            channelState = JSON.parse(currentState.toString());
        }
    } catch (e) { }

    // If we couldn't load the details then create a new channel.
    if (!channelState) {
        channelState = createChannel(generateSeed(81), 2, mode, sideKey)
    }

    // Create a MAM message using the channel state.
    const mamMessage = createMessage(channelState, TrytesHelper.fromAscii(asciiMessage));

    // Display the details for the MAM message.
    console.log('Seed:', channelState.seed);
    console.log('Address:', mamMessage.address);
    console.log('Root:', mamMessage.root);
    console.log('NextRoot:', channelState.nextRoot);

    // Decode the message using the root and sideKey.
    // The decode is for demonstration purposes, there is no reason to decode at this point.
    const decodedMessage = parseMessage(mamMessage.payload, mamMessage.root, sideKey);

    // Display the decoded data.
    console.log('Decoded NextRoot', decodedMessage.nextRoot);
    console.log('Decoded Message', decodedMessage.message);

    // Store the channel state.
    try {
        fs.writeFileSync('./channelState.json', JSON.stringify(channelState, undefined, "\t"));
    } catch (e) {
        console.error(e)
    }

    // So far we have shown how to create and parse a message
    // but now we actually want to attach the message to the tangle
    const node = "https://chrysalis-nodes.iota.org";
    const explorerRoot = "https://explorer.iota.org/mainnet";

    // Attach the message.
    console.log('Attaching to tangle, please wait...')
    const { messageId } = await mamAttach(new SingleNodeClient(node), mamMessage, "MY9MAM");
    console.log(`Message Id`, messageId);
    console.log(`You can view the stored message here ${explorerRoot}/message/${messageId}`);
    console.log(`You can view the mam channel here ${explorerRoot}/streams/0/${mamMessage.root}/${mode}/${sideKey}`);

    // Try fetching it as well.
    console.log('Fetching from tangle, please wait...');
    const fetched = await mamFetch(node, mamMessage.root, mode, sideKey)
    if (fetched) {
        console.log('Fetched Root', fetched.root);
        console.log('Fetched', TrytesHelper.toAscii(fetched.message));
        console.log('Fetched Next Root', fetched.nextRoot);
    } else {
        console.log('Nothing was fetched from the MAM channel');
    }
}

function generateSeed(length) {
    const charset = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ9';
    let seed = '';
    while (seed.length < length) {
        const byte = crypto.randomBytes(1)
        if (byte[0] < 243) {
            seed += charset.charAt(byte[0] % 27);
        }
    }
    return seed;
}

run("Hello MAM World!")
    .then(() => console.log("done"))
    .catch((err) => console.error(err));