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05 February 2026 22:07

Use prettierd as a formatter in apheleia

I use emacs v30.2. And within that, [apheleia](https://github.com/radian-software/apheleia) for its reformat-on-save magic.

For Javascript I had been using [prettier](https://github.com/prettier/prettier) as the formatter. Which works, AND, on my old creaky laptop (Windows), it's noticeably slower than on my more powerful workstation at work (Linux). The effect is that after save, there is a about-one-second delay during which the reformat is pending. This can be... distracting.

So I looked into [prettierd](https://github.com/fsouza/prettierd); using an idea cribbed from [eslint_d](https://github.com/mantoni/eslint_d.js), it daemonizes prettier so that it does not have to start each time it runs. The idea is that the first time it runs, it will be slow, as slow as running just prettier. But on subsequent runs, the prettier process is still running in the background, so you don't pay the startup cost. Which makes the whole experience snappier. I didn't measure but it made a clear, substantial improvement for me.

The README for prettier included information for how to set it up for neovim but I didn't find anything for emacs. When I tried I had some trouble, at first, because I didn't have the arguments quite right.

Eventually I found that this worked:

```
(use-package apheleia
:ensure t
:defer t
:config
;; prettierd supports reading options from the command
;; line if you use the --key=value format. It will also read options
;; from .prettierrc , but by default prefers the command-line options.
;; Contents of that file might be: { "parser": "babel-flow", "tabWidth": 2 }
(eval-when-compile (defvar apheleia-formatters))
(if-let* ((prettierd (executable-find "prettierd")))
(setf (alist-get 'prettier-javascript apheleia-formatters)
'("prettierd" filepath "--parser=babel-flow"
(s-join "=" (apheleia-formatters-js-indent "--use-tabs" "--tab-width")))))
)
```
`s-join` is needed there because prettierd does not accept options like `--tab-with 2`; it requires `--tab-width=2` . ([more on this](https://github.com/fsouza/prettierd/issues/982#issuecomment-3850094394))

The above requires that I previously installed prettierd globally like so:
```
npm install -g @fsouza/prettierd
```

Which means you need node and npm installed, etc.

This is working on emacs on Windows 11. I do not use WSL. But because apheleia requires a diff that supports `--rcs` , I need unix utilities to be on PATH. I use git, so conveniently, I can just put the dir for its utilities (`C:\Program Files\Git\usr\bin`) on my PATH.

One notable downside is that prettierd does not provide process management. It does not auto-stop the daemon on idle ([cite](https://github.com/fsouza/prettierd/issues/645)). You must figure out if and when to stop it, and then actually stop it, on your own, if you wish. There will be one prettier running for each directory in which you run apheleia. This may be a significant downside.

The progenitor project, eslint_d, has introduced a feature to kill the underlying eslint process after some period of idleness, by default 15 minutes. prettierd does not have this feature. Yet?

https://redd.it/1qwsgv1
@r_emacs