Kubernetes is an orchestrator, it is not a language such as JavaScript, you can create a javascript app, and then create a docker image containing the said app which you can then run in a kubernetes cluster.

I must say though, that your question makes me wonder if you have any experience in how containers or orchestrators work, which makes me think I should recommend you to read up a bit more and play around a bit more with it before trying to run it on a live environment.

If you don't want to listen to the above, you will basically need the following:

• A deployment, with a pod running your container with the app inside.
• A service, exposing the deployment to the cluster.
• An ingress(route), exposing your service to the outside net.

There are other ways to do it, but k8s is not an "easy thing" to work with, it requires quite a bit of research and testing to allow you to know what you are doing before it is useful.

Start with learning to use Docker. Containers is mostly "a way" to run processes in an isolated environment, so to do anything in a container, you need to do that with a process, e.g. bash or a custom application.

You can run both commands and services in a Docker container.

When deploying apps to Kubernetes, it is services, e.g. a web server listening on a port. But you can also run commands on Kubernetes by using Jobs

Here is a "hello world" Job using bash:

apiVersion: batch/v1
kind: Job
metadata:
  name: hello-world
spec:
  template:
    metadata:
      name: hello-world
    spec:
      containers:
      - name: hello-world
        image: centos:7
        command:
         - "bin/bash"
         - "-c"
         - "echo hello world"
      restartPolicy: Never