Why isn't process.stdout an instanceof fs.WriteStream?

[tcodes0]

• Node.js Version: 14.9.0
• OS: Linux Arch7 5.8.7-arch1-1 Update README for help #1 SMP PREEMPT Sat, 05 Sep 2020 12:31:32 +0000 x86_64 GNU/Linux
• Scope (install, code, runtime, meta, other?): runtime
• Module (and version) (if relevant): fs

> let s = require('fs').WriteStream
undefined
> s
[Function: WriteStream]
> process.stdout instanceof s
false
> process.stdout
<ref *1> WriteStream {
 ...
> process.stdout.constructor.name
'WriteStream'

this is confusing because process.stdout appears to be a WriteStream as far as I can tell.

[devsnek]

It is a WriteStream, just not a fs WriteStream. Check out https://nodejs.org/api/tty.html#tty_class_tty_writestream.