install node.js in docker container

[magicxor]

see yt-dlp/yt-dlp#15012

With the release of yt-dlp version 2025.11.12, external JavaScript runtime support has arrived.
All users who intend to use yt-dlp with YouTube are strongly encouraged to install one of the supported JS runtimes.

[Copilot]

Pull Request Overview

This PR adds Node.js runtime support to the Docker container to comply with yt-dlp version 2025.11.12 requirements for YouTube downloads. The implementation uses fnm (Fast Node Manager) to install the LTS version of Node.js.

Key Changes:

• Installs Node.js LTS using fnm (Fast Node Manager)
• Changes the default shell to enable fnm's bash login initialization
• Adds the unzip package to system dependencies

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[Copilot]

The SHELL change to use --login shell affects all subsequent RUN commands in the Dockerfile, including the poetry installation at line 34. This could cause unexpected behavior or performance issues as login shells source additional configuration files.

Consider one of these approaches:

1. Revert SHELL after the Node.js installation is complete
2. Set up fnm's PATH manually without requiring a login shell
3. Use a single RUN command with explicit shell invocation for just the fnm commands

Example for approach 2:

RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get install -y curl ffmpeg unzip && \
    curl -o- https://fnm.vercel.app/install | bash && \
    export PATH="/root/.local/share/fnm:$PATH" && \
    eval "$(fnm env)" && \
    fnm install --lts && \
    node -v && npm -v && \
    python -m pip install --upgrade pip && \
    apt-get clean && rm -rf /var/lib/apt/lists/* && \
    mkdir /app

Suggested change

	curl -o- https://fnm.vercel.app/install | bash
	SHELL ["/bin/bash", "--login", "-c"]
	RUN fnm install --lts && \
	curl -o- https://fnm.vercel.app/install | bash && \
	export PATH="/root/.local/share/fnm:$PATH" && \
	eval "$(fnm env)" && \
	fnm install --lts && \

[Copilot]

Splitting the RUN command into two separate RUN statements creates an additional Docker layer and prevents proper cleanup. The apt-get clean && rm -rf /var/lib/apt/lists/* on line 30 runs in a separate layer from the apt-get install on line 23, so it doesn't actually reduce the image size.

Docker layers are immutable, so removing files in a later layer doesn't remove them from earlier layers. To effectively reduce image size, the installation and cleanup should be in the same RUN command.

Consider combining these RUN commands back together as suggested in the previous comment.

[Copilot]

The fnm installation adds Node.js to the build environment but doesn't ensure it's available in the runtime environment. The fnm tool modifies the shell's PATH through .bashrc, which works with the --login shell, but this doesn't guarantee Node.js will be available when the container runs the CMD.

To ensure Node.js is available at runtime, add:

ENV PATH="/root/.local/share/fnm:$PATH"

after the fnm installation, or configure fnm to install Node.js to a permanent location that's added to the PATH environment variable.

[Copilot]

[nitpick] The unzip package is added but there's no clear indication in the PR description or code why it's needed. If it's a dependency for fnm or Node.js installation, please document this in a comment. If it's unrelated to the Node.js installation, consider adding it in a separate commit or PR for clarity.

Suggested change

	# 'unzip' is required for fnm/Node.js installation scripts

[Copilot]

[nitpick] Extra trailing whitespace after npm -v. This should be removed for consistency.

Suggested change

	npm -v && \
	npm -v && \