nats.js/jetstream/examples/04_consume.js

/*
 * Copyright 2023 The NATS Authors
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { connect } from "@nats-io/transport-deno";
import { jetstream } from "@nats-io/jetstream";
import { setupStreamAndConsumer } from "./util.js";

// create a connection
const nc = await connect();

// create a stream with a random name with some messages and a consumer
const { stream, consumer } = await setupStreamAndConsumer(nc);

// retrieve an existing consumer
const js = jetstream(nc);
const c = await js.consumers.get(stream, consumer);

// the consumer is wrapped in loop because this way, if there's some failure
// it will re-setup consume, and carry on.
// this is the basic pattern for processing messages forever
while (true) {
  console.log("waiting for messages");
  const messages = await c.consume();
  try {
    for await (const m of messages) {
      console.log(m.seq);
      m.ack();
    }
  } catch (err) {
    console.log(`consume failed: ${err.message}`);
  }
}