passthrough-writable.js

const Duplexify = require('duplexify')
const clone = require('cloneable-readable')

class PassthroughWritable extends Duplexify {
  constructor (ws) {
    super()
    const pt = new stream.PassThrough()
    this.setWritable(stream.pipeline(pt, ws))
    this.setReadable(clone(pt))
  }
}