prettier-js for Emacs

This Emacs package provides a function, prettier-js-prettify, which formats the current buffer using Prettier. It also exports a minor mode, prettier-js-mode, which calls prettier-js-prettify on save.

Despite the "-js" in its name, this package actually supports more than just JavaScript. It works with any language that Prettier supports! List here.

Configuration

Requirements

Have prettier installed

Ensure that the prettier program is installed:

which prettier

If prettier is not installed already, you can install it using npm install -g prettier or via your package manager.

Alternatively, if your project uses Prettier (i.e. it's a devDependency in your package.json), then you'll be able to use the executable installed via npm install, instead.

Have diff installed

This package uses the diff program under the hood to reliably identify formatting changes made by Prettier. On macOS and GNU/Linux, diff should already be installed. On other platforms, you should install/configure GNU's diff implementation.

Windows

On Windows, install via Chocolatey:

1. Follow the Chocolatey install instructions: https://chocolatey.org/install
2. Open an Admin PowerShell session
3. Install the diff program: choco install diffutils

Also, make sure that the correct version of diff is accessible from your system path; sometimes, multiple conflicting diff executables may be installed.

BSD systems (OpenBSD, FreeBSD)

On BSD systems (like OpenBSD, FreeBSD), the default diff program may not support some GNU diff features that this package requires, such as --strip-trailing-cr. To resolve this:

1. Install GNU diff (often called gdiff or gnudiff):
   • On OpenBSD: pkg_add gdiff
   • On FreeBSD: pkg install diffutils
2. Configure this package to use the GNU diff implementation:

   (setq prettier-js-diff-command "gdiff")

   (Use the appropriate command name for your system, which might be gdiff, gnudiff, or gd)

Ensure Emacs' path is configured correctly

Depending on how the programs are installed, node, prettier, and/or diff may be missing on Emacs' exec-path. When attempting to format a buffer, this could result in errors such as:

• "Node executable not found"
• "Could not find prettier executable"

An easy solution to this issue is to install and use exec-path-from-shell. Add to your init file:

(exec-path-from-shell-initialize)

Basic configuration

First require the package:

(require 'prettier-js)

Or use use-package (available in Emacs 29.1 and above):

(use-package prettier-js)

Then you can hook into any modes where you want to format with Prettier:

(add-hook 'js-mode-hook 'prettier-js-mode)
(add-hook 'web-mode-hook 'prettier-js-mode)

You can also enable use of your project's Prettier (instead of the system one):

(setq prettier-js-use-modules-bin t)

This uses node_modules/.bin/prettier. Make sure to run npm install from your project directory so that the command is available there.

Enable/disable per project

Say that you only want to use Prettier with certain projects. Instead of configuring Emacs with (add-hook 'some-mode-hook 'prettier-js-mode), you could check for the presence of a config file:

(defun maybe-use-prettier ()
  "Enable `prettier-js-mode' if an rc file is located."
  (if (locate-dominating-file default-directory ".prettierrc")
      (prettier-js-mode +1)))

(add-hook 'js-mode-hook 'maybe-use-prettier)

Alternatively, say that you want to use Prettier everywhere by default, except for when editing files in certain directories. Use (add-hook 'some-mode-hook 'prettier-js-mode), and in directories where you want Prettier disabled, add a .dir-locals.el file with the following contents:

((nil . ((eval . (prettier-js-mode 0)))))

Prettier arguments

To adjust the CLI args used for the prettier command, you can customize the prettier-js-args variable. This may be useful for controlling specific program behaviors; for instance:

(setq prettier-js-args '("--no-editorconfig"))

While it's possible to control formatting options with flags like --single-quote, it's usually better to use a configuration file.

Usage with web-mode

web-mode is a popular mode for editing .js and .jsx files, but it is used to edit other template files too. If you want to hook prettier-js-mode into web-mode for .js and .jsx files only, you can define a helper function like this:

(defun enable-minor-mode (my-pair)
  "Enable minor mode if filename match the regexp.
MY-PAIR is a cons cell (regexp . minor-mode)."
  (if (buffer-file-name)
      (if (string-match (car my-pair) buffer-file-name)
          (funcall (cdr my-pair)))))

And then hook into web-mode like this:

(add-hook 'web-mode-hook #'(lambda ()
                            (enable-minor-mode
                             '("\\.jsx?\\'" . prettier-js-mode))))

Usage with prettierd

If you want to mostly eliminate the overhead of running the prettier command on every file save (improving performance slightly), you could try using prettierd to run Prettier as a daemon.

(setq prettier-js-command "prettierd")

Note that this may come at the expense of a bit more complexity in terms of configuring/managing the daemon.

Available commands

• M-x prettier-js-prettify formats the current buffer. In org-mode, it formats all the code blocks in the buffer.
• M-x prettier-js-prettify-region formats the current region
• M-x prettier-js-prettify-code-block formats the code block at point (in org-mode)

Customization

This package is customizable via Emacs' easy customization interface:

M-x customize-group prettier-js

• prettier-js-command is the prettier executable to use
• prettier-js-diff-command is the diff executable to use
• prettier-js-args are the args passed to the prettier command
• prettier-js-use-modules-bin enables use of node_modules/.bin/prettier (your project's Prettier version)
• prettier-js-show-errors customizes where to display the error output (buffer, echo or nil)
• prettier-js-width-mode customizes the width when formatting buffer contents (window, fill or nil)