Q:

How can i capture stdout from dockerode when using promises?

I am trying to run a docker container using dockerode following the examples here. 
The issue I am having is that the output of the container prints to stdout, but I am trying to capture it and store it in a variable while using promises if possible. 
My code is:
const Docker = require('dockerode');

const docker = new Docker();

docker
    .run(
        'wappalyzer/cli',
        ['https://www.wappalyzer.com'],
        [process.stdout, process.stderr],
        { Tty: false }
    )
    .then((data) => {
        let output = data[0];
        let container = data[1];
        console.log(typeof output);
        console.log(output);
        return container.remove();
    })
    .catch((error) => console.log(error));

A:

For docker.run(), The [ process.stdout, process.stderr ] streams are where the underlying stdio data is piped to.
Change these arguments to writable streams you control. You can use something like a memory stream, a file or implement a stream yourself. 
const Docker = require('dockerode')
const streams = require('memory-streams')

const docker = new Docker()
const stdout = new streams.WritableStream()
const stderr = new streams.WritableStream()

docker.run(
    'debian:10',
    ['sh', '-c', 'echo test; echo testerr >/dev/stderr; echo test3'],
    [stdout, stderr],
    { Tty: false }
  )
  .then(([ res, container ]) => {
      console.log(res)
      console.log('stdout: %j', stdout.toString())
      console.log('stderr: %j', stderr.toString())
      return container.remove()
  })
  .catch((error) => console.log(error))

