using NATs how can I create a durable consumer that constantly listens for new messages

I have this function in javascript that given a durable consumer fetches messages and triggers a callback function:

export const consumeMessages = async (callback, consumer) => {
    const iter = await consumer.fetch({ max_messages: 1 });

    (async () => {
        for await (const m of iter) {
            await callback(m.subject, m.data);
            m.ack()
        }
    })();
    return iter
};

consumeMessages is triggered once on booting up of my app:

            await jsm.consumers.add(config.NATS_STREAM_NAME, {
                ack_policy: AckPolicy.Explicit,
                durable_name: sessionId,
                filter_subject: subject,
            });
            const consumer = await js.consumers.get(config.NATS_STREAM_NAME, sessionId);

            const iter = await consumeMessages(receiveMessages, consumer);
    

This works but only retrieves 1 message. I want to consumer to keep retrieving messages that come in.

I understand that this is happening because of this line await consumer.fetch({ max_messages: 1 });

But I cannot find another way to do this from the documentation. I do not want to hardcode a mac_messages value since I want consumer to keep fethching until it is deleted.