switch-writable

Dynamically select a stream's writable target.
Adapted from switchstream.

Usage

const Switch = require('switch-writable')
const from = require('from2-array').obj
const fs = require('fs')

from(['a', 'b', 'a', 'a'])
  .pipe(Switch(data => {
    if (data === 'a') return 'a'
    if (data === 'b') return 'b'
  }).between({
    a: fs.createWriteStream('a.txt'), // 'aaa'
    b: fs.createWriteStream('b.txt') // 'b'
  }))

If the stream or any of the target streams error or close prematurely, all other streams are destroyed. This also happens if the switch function returns a key for which there is no stream (e.g. c in the example above).

Target streams can be created lazily:

Switch(data => {
  if (data === 'a') return 'a'
  if (data === 'b') return 'b'
}).between({
  a: () => fs.createWriteStream('a.txt'),
  b: () => fs.createWriteStream('b.txt')
})

The list of streams can be an array:

Switch(data => {
  if (data === 'a') return 0
  if (data === 'b') return 1
}).between([
  fs.createWriteStream('a.txt'),
  fs.createWriteStream('b.txt')
])

Lastly, a default key can be provided, for when no stream matches the key or when no key is returned:

Switch({ default: 1 }, (data) => null).between([
  fs.createWriteStream('a.txt'),
  fs.createWriteStream('b.txt')
])

Other differences from switchstream

• Is and takes a writable stream instead of a duplex stream
• Has backpressure (is as slow as the slowest target)
• Has and expects destroy() semantics of Node 8+
• Doesn't coerce keys to the right type (string or number)
• Doesn't support async map function.

Licence

MIT © 2018-present Vincent Weevers. Adapted from switchstream © Tim Oxley.