xreq | Extended require for nodejs | Runtime Evironment library

You have to wait for the response, because it can take a while:

The function you pass to socket.on is called when the connection is ready.

You aren't using a function declaration. You aren't creating a variable called setUsername that you can access later.

Remove the onclick attribute. They are generally more trouble then they are worth and are rather unhelpful here.

Change the function you pass to socket.on to one which finds the button in the DOM (e.g. with document.querySelector) and then using addEventListener to attach a (click) event handler to it.

Do the work you are currently doing in setUsername inside that event handler instead (i.e. when the button is clicked).

Because security reasons you cannot make javascript request to external domain. This is possible only if external allow to do that by adding this header: Access-Control-Allow-Origin.

For your issue the best will be just use ajax to read static file from local.

Here's what worked:

May be I did not get your point of view exactly, but having a few years spent inside ZeroMQ based distributed-systems, I can address a few misses in the concept.

First:
Yes, Zen-of-Zero does provide ZERO-Warranty for a respective message delivery. This may seem surprising, but there are many reasons for working this way and no other. There is a warranty of consistency - i.e. a message is either delivered as-is or none at all. This means, if the message has made it through the socket, the receiving side may be sure, that the sender was dispatching this very content and no error-checking need be put in place, as the ZeroMQ has already spent all its effort to deliver a 1:1 bit-by-bit copy of the original.

Next:
ZeroMQ is designed as a Broker-less asynchronous lightweight signalling / messaging tool. The word Broker-less means, there are zero-efforts spend for any sort of a tool-based persistence, so indeed there is no care about any Broker-side storing any (semi-)persistent replica(s) of the messages, be it those delivered or those not delivered due to whatever technical reason ( yet, those delivered are -- as expressed above -- guaranteed to be OK and an exact copy of the original ).

Implication:
this means, there will be zero effect from designing a zmq.device( zmq.Queue, f, b ) as this will have all the properties reported above, so it will principally live under the same set of paradigms.

If one needs to have both the delivered content-warranty and also the all-messages-delivered warranty, the former is included in the ZeroMQ tools since inception, the latter is to be added on top of the standard tools, as an extended supra-pattern, re-using the delivery-agnostic standard tools.

This way one can get what you have sketched above, yet not wasting a single CPU-clock in all other use-cases, where delivery-agnostic, just "best-effort" transports are okay.

Given the above narrative, the story of "How to effectively ..." ( where a metric of what and how actually measures the desired effectivity may get some further clarification later ), turns into another question - "Can we re-factor the ZeroMQ Signalling / Messaging infrastructure, so as to work without using as many IP-addresses:port#-s as would the tcp://-transport-class based topology actually need?"

Upon an explicitly expressed limit of having not more than a just one IP:PORT# per host/node ( being thus the architecture's / desing's the very, if not the most expensive resource ) one will have to overcome a lot troubles on such a way forward.

It is fair to note, that any such attempt will come at an extra cost to be paid. There will not be any magic wand to "bypass" such a principal limit expressed above. So get ready to indeed pay the costs.

It reminds me one Project in TELCO, where a distributed-system was operated in a similar manner with a similar original motivation. Each node had an ssh/sshd service setup, where local-port forwarding enabled to expose a just one publicly accessible IP:PORT# access-point and all the rest was implemented "inside" a mesh of all the topological links going through ssh-tunnels not just because the encryption service, but right due to the comfort of having the ability to maintain all the local-port-forwarding towards specific remote-ports as a means of how to setup and operate such exclusive peer-to-peer links between all the service-nodes, yet having just a single public access IP:PORT# per node.

If no other approach will seem feasible _{( PUB/SUB being evicted for either traffic actually flowing to each terminal node in cases of older ZeroMQ/API versions, where Topic-filtering gets processed but on the SUB-side, which both security and network Departments will not like to support, or for concentrated workloads and immense resources needs on PUB-side, in cases of newer ZeroMQ/API versions, where Topic-filter is being processed on the sender's side. Adressing, dynamic network peer (re-)discovery, maintenance, resources planning, fault resilience, ..., yes, not any easy shortcut seems to be anywhere near to just grab and (re-)use )} the above mentioned "stone-age" ssh/sshd-port-forwarding with ZeroMQ, running against such local-ports only, may save you.

Anyway - Good Luck on the hunt!

XREQ/XREP are aliases for ROUTER/DEALER. XREQ/XREP were used in ZeroMQ 2.x.