Hedera Consensus Service (code example)

.env

OPERATOR_ID=
OPERATOR_PVKEY=

index.js

require("dotenv").config();

const {
  AccountId,
  PrivateKey,
  Client,
  TopicCreateTransaction,
  TopicMessageQuery,
  TopicMessageSubmitTransaction,
} = require("@hashgraph/sdk")

// Configure accounts and client, and generate needed keys
const operatorId = AccountId.fromString(process.env.OPERATOR_ID);
const operatorKey = PrivateKey.fromString(process.env.OPERATOR_PVKEY);
const client = Client.forTestnet().setOperator(operatorId, operatorKey);

async function main() {
  // Create a new public topic
  let txResponse = await new TopicCreateTransaction().execute(client);

  // Grab the topic ID
  let receipt = await txResponse.getReceipt(client);
  let topicId = receipt.topicId;
  console.log(`Your topic ID is: ${topicId}`)

  // Wait 5 seconds between consensus topic creation and subscription creation
  await new Promise((resolve) => setTimeout(resolve, 5000));
  
  // Subscribe to the topic
  new TopicMessageQuery()
    .setTopicId(topicId)
    .subscribe(client, (message) => {
      let messageAsString = Buffer.from(message.contents, "utf8").toString();
      console.log(
        `${message.consensusTimestamp.toDate()} - Sequence number: ${message.sequenceNumber} - ${messageAsString}`
      )
    })

  // Submit a message
  let sendResponse = await new TopicMessageSubmitTransaction({
    topicId: topicId,
    message: "Hello, HCS!"
  }).execute(client);

  // Get the receipt of the transaction
  const getReceipt = await sendResponse.getReceipt(client);
  
  // Get the status of the transaction
  const txStatus = getReceipt.status;
  console.log(`Status: ${txStatus.toString()}`)

  client.close();
}

main();

package.json

{
  "name": "hedera-consenus-service",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "Michiel Mulders",
  "license": "ISC",
  "dependencies": {
    "@hashgraph/sdk": "^2.22.0",
    "dotenv": "^16.0.3"
  }
}

subscribe.js

require("dotenv").config();

const {
  AccountId,
  PrivateKey,
  Client,
  TopicMessageQuery,
} = require("@hashgraph/sdk")

// Configure accounts and client, and generate needed keys
const operatorId = AccountId.fromString(process.env.OPERATOR_ID);
const operatorKey = PrivateKey.fromString(process.env.OPERATOR_PVKEY);
const client = Client.forTestnet().setOperator(operatorId, operatorKey);

async function main() {
  let topicId = "0.0.4049400";
  let consensusTimestampMsg2 = "1681383435.529633099"
  
  // Subscribe to the topic
  new TopicMessageQuery()
    .setTopicId(topicId)
    .setStartTime(consensusTimestampMsg2)
    // .setEndTime(timestamp)
    // .setLimit(10)
    .subscribe(client, (message) => {
      console.log(`Seq number: ${message.sequenceNumber}`)
    })
}

main();