eolas/zk/Ports.md

---
categories:
  - Programming Languages
tags:
  - backend
  - node-js
---

# Ports

When working in development we are able to specify the specific port from which
we want top serve our application. In production, we do not always have this
control: the port will most likely be set by the provider of the server
environment.

While we may not know the specific port, whatever it is, it will be accessible
via the `PORT` environment variable. So we can use this when writing our
[event listeners](Events%20module.md#event-emitters):

```js
const port = process.env.PORT || 3000;
```

This way, if a port is set by the provider it will use it. If not, it will fall
back to 3000.