Piping any stdout from node.js to fx stdin causes non-functional UI state

[jwhiting]

node -e 'process.stdout.write(JSON.stringify({"a":1}))' | fx

Running this command on MacOS Tahoe, and Ubuntu 22 LTS, with fx installed via homebrew at v39.2.0 shows the json in the TUI, but the interactivity is in a non-functional state. All key presses are rendered at the bottom of the screen and overwrite the highlighted character space reserved for showing the selected json element path.

I surfaced this while trying to use fx to debug output of a node.js CLI utility that outputs json. I assumed this was a bug in my own CLI program, until I realized finally it could be reproduced with even trivial output from node.js. I was unable to have node produce output that did NOT produce the broken UI state when piped to fx. If I pipe to a file, then cat that, no problem:

node -e 'process.stdout.write(JSON.stringify({"a":1}))' > test.json && cat test.json | fx works just fine

[antonmedv]

node -e 'process.stdout.write(JSON.stringify({"a":1}))' | fx

tested on windows and macos. seems works for me.

[mohamedkamal9918]

node -e 'process.stdout.write(JSON.stringify({"a":1}))' | fx

tested on Windows and macOS. Seems to work for me.

node -e 'process.stdout.write(JSON.stringify({"a":1}))' | fx

عند تشغيل هذا الأمر على نظامي macOS Tahoe وUbuntu 22 LTS، مع تثبيت fx عبر Homebrew بالإصدار 39.2.0، يظهر ملف JSON في واجهة المستخدم النصية، لكن التفاعل مع البرنامج معطل. تُعرض جميع ضغطات المفاتيح في أسفل الشاشة، وتُستبدل المساحة المخصصة لعرض مسار عنصر JSON المحدد.

اكتشفتُ هذه المشكلة أثناء محاولتي استخدام fx لتصحيح أخطاء مُخرَجات أداة سطر أوامر Node.js التي تُخرِج بيانات JSON. ظننتُ في البداية أنها خللٌ في برنامج سطر الأوامر الخاص بي، إلى أن أدركتُ أخيرًا أنه يُمكن إعادة إنتاجها حتى مع مُخرَجات بسيطة من Node.js. لم أتمكن من جعل Node.js يُخرِج بيانات لا تُؤدِّي إلى حالة واجهة المستخدم المعطوبة عند تمريرها إلى fx.

أما إذا مررتُ البيانات إلى ملف، ثم استخدمتُ الأمر cat لعرض محتوياته، فلا توجد أي مشكلة.

node -e 'process.stdout.write(JSON.stringify({"a":1}))' > test.json && cat test.json | fx يعمل بشكل جيد

[jwhiting]

tested on windows and macos. seems works for me.

Did you test the keyboard navigation specifically? It renders, but is not responsive to key navigation. Reproducible on multiple separate machines and OSes on my end.

[antonmedv]

Hmm, could you please specify what os version? What terminal as well? Terminal.app? What shell zsh or bash?

[jwhiting]

On my macbook pro the behavior occurs on zsh 5.9 (arm64-apple-darwin25.0) and GNU bash, version 3.2.57(1)-release (arm64-apple-darwin25) and with both the latest iTerm, Ghostty, and in mac os Terminal.app. I can reproduce it with zsh -f (to eliminate any rc files potentially polluting shell behavior). I have node installed via nvm, using version 22.22.0 but switching to v24 has the same behavior.

On Ubuntu 24.04.3 LTS with bash GNU bash 5.2.21(1)-release the behavior is erratic now that I test it more. Sometimes it actually does work, while other times it dies immediately and echoes leaked terminal escape sequences back onto the shell.

$ node -e 'process.stdout.write(JSON.stringify({"a":1}))' | fx
^[]11;rgb:0d83/1041/142b^[\^[[48;1R

I don't have other machines to test on at the moment. That this isn't occurring for others does have me wondering if there's something with my two hosts here. So I created a dockerfile to try this out:

FROM node:22-bookworm

RUN apt-get update && apt-get install -y \
    build-essential \
    curl \
    file \
    git \
    procps \
    sudo \
  && rm -rf /var/lib/apt/lists/*

RUN useradd -m -s /bin/bash linuxbrew \
  && echo 'linuxbrew ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers

USER linuxbrew
WORKDIR /home/linuxbrew

RUN /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

ENV PATH="/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin:${PATH}"

RUN brew install fx \
  && brew --version \
  && node --version \
  && npm --version \
  && fx --version

CMD ["bash"]

Built that container (docker build -t node22-brew-fx path/to/dockerfile) then launched a bash shell in it (docker run --rm -it node22-brew-fx bash ), and it's still happening in that environment. Hopefully you can reproduce it this way.

[antonmedv]

I tested on zsh 5.9 (arm64-apple-darwin25.0) and Ghostty 1.3.1, on node26 and deno2.8.3 for me it works. I guess there are some problems in our TUI library https://github.com/charmbracelet/bubbletea

Maybe you could create an issue there?