Add option for Nodejs path like BUN_PATH

[kraanzu]

Describe the bug
Reflex tries to install the required node version by itself into data directory but this fails on systems like NixOS or Guix because its not allowed to run binaries directly

NixOS cannot run dynamically linked executables intended for generic
linux environments out of the box. For more information, see:
https://nix.dev/permalink/stub-ld

To Reproduce

• reflex init and choose any template
• reflex run

Expected behavior
Reflex runs without any errors just like in the documentation

Specifics (please complete the following information):

• Python Version: Python 3.12.5
• Reflex Version: 0.5.10
• OS: NixOS 22.04

Additional context
Related issue: #1470

[Lendemor]

Here is the function we run when searching for node.

def get_node_path() -> str | None:
    """Get the node binary path.

    Returns:
        The path to the node binary file.
    """
    node_path = Path(constants.Node.PATH)
    if not node_path.exists():
        return str(which("node"))
    return str(node_path)

So if node is missing from the reflex data folder, it should try to find wherever you have it installed at the moment.

[kraanzu]

Hmm... I checked and it seems to return a path that is OK

In [2]: get_node_path()
Out[2]: '/run/current-system/sw/bin/node'

In my case, The data directory is ~/.local/share/reflex/, and if I were to delete this, then it should use the which("node") but that is not the case, it re-installs the node binary and then the function above returns something different

In [2]: get_node_path()
Out[2]: '/home/kraanzu/.local/share/reflex/fnm/node-versions/v18.17.0/installation/bin/node'

and hence the error. I'll do a bit more digging on this

[kraanzu]

I think this function is the issue while deciding whether to install node or not:

def check_node_version() -> bool:
    """Check the version of Node.js.

    Returns:
        Whether the version of Node.js is valid.
    """
    current_version = get_node_version()
    if current_version:
        # Compare the version numbers
        return (
            current_version >= version.parse(constants.Node.MIN_VERSION)
            if constants.IS_WINDOWS
            else current_version == version.parse(constants.Node.VERSION)
        )
    return False

I'm currently using node version 18.20.4 which was the last version before they moved to 19.x

The function above checks for total equality which causes the problem here, even the patch version update will return a False and will result in installing Node separately