prettier-js is a function that formats the current buffer using prettier. The package also exports a minor mode that applies (prettier-js) on save.

Ensure that the prettier program is installed:

which prettier

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

First require the package:

(require 'prettier-js)

Then you can hook to your favorite javascript mode:

(add-hook 'js2-mode-hook 'prettier-js-mode)
(add-hook 'web-mode-hook 'prettier-js-mode)
...

To adjust the CLI args used for the prettier command, you can customize the prettier-js-args variable:

(setq prettier-js-args '(
  "--trailing-comma" "all"
  "--bracket-spacing" "false"
))

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 to 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 to web-mode like this:

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

This package requires the diff tool which is already included on Unix platforms. The simplest way to install diff on Windows is to use Chocolatey. The steps are as follows:

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

You should now be able to open Emacs and successfully use this package.

This package is customizable via custom.el:

M-x customize-group prettier-js

• prettier-js-command is the prettier command
• prettier-js-args are the args passed to the prettier command
• 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)

If you want to use your project's prettier version you can rely on https://github.com/codesuki/add-node-modules-path

(eval-after-load 'web-mode
    '(progn
       (add-hook 'web-mode-hook #'add-node-modules-path)
       (add-hook 'web-mode-hook #'prettier-js-mode)))