worker_threads in node.js report supportsColor false

[mdouglass]

In worker threads, supports-color is unable to automatically detect color support.

const { Worker, isMainThread } = require('worker_threads')
const supportsColor = require('supports-color')

if (isMainThread) {
  console.log('mainThread, supportsColor.stdout', supportsColor.stdout)
  console.log('mainThread, supportsColor.stderr', supportsColor.stderr)
  new Worker(__filename)
} else {
  console.log('workerThread, supportsColor.stdout', supportsColor.stdout)
  console.log('workerThread, supportsColor.stderr', supportsColor.stderr)
}

$ node ./main.js 
mainThread, supportsColor.stdout { level: 2, hasBasic: true, has256: true, has16m: false }
mainThread, supportsColor.stderr { level: 2, hasBasic: true, has256: true, has16m: false }
workerThread, supportsColor.stdout false
workerThread, supportsColor.stderr false

It looks like the stream type in worker threads is WritableWorkerStdio which returns isTTY false so the check at:

supports-color/index.js

Line 57 in 14a0e6f

if (stream && !stream.isTTY && forceColor === undefined) {

fails. If I skip that check (with stream.constructor.name === 'WritableWorkerStdio') then supportsColor returns correct information and color output does work. I'm not sure if that's the best fix or whether it even should be fixed.

[Qix-]

Ehhh depends. I've not yet used worker threads, so I'm not 100% sure, but if their stdio handles map to TTY handles they should probably report isatty==1.

Might be worth seeing if node has an issue open for it.