Emacs: Format JavaScript Code 📜

put this in your Emacs Init File:

(defun xah-js-format-buffer ()
  "Format JavaScript/TypeScript code of current buffer.
Buffer is saved first.
This command requires external command deno.

URL `http://xahlee.info/emacs/emacs/emacs_format_js_code.html'
Created: 2020-09-23
Version: 2025-07-02"
  (interactive)
  (when (not buffer-file-name) (user-error "buffer %s is not a file." (buffer-name)))
  (when (buffer-modified-p) (save-buffer))
  (let ((xbackupName (concat buffer-file-name "." (format-time-string "%Y%m%d%H%M%S") "~")))
    (copy-file buffer-file-name xbackupName t)
    (message (concat "\nBackup saved at: " xbackupName)))
  (let ((xpos (point))
        (xoutbuf (get-buffer-create "*xah-js-format output*"))
        xexitstatus)
    (setq xexitstatus (call-process "deno" nil xoutbuf nil "fmt" buffer-file-name "--quiet"))
    (if (eq 0 xexitstatus)
        (progn
          (revert-buffer t t t)
          (goto-char xpos))
      (progn
        (display-buffer xoutbuf)
        (error "error xah-html-format-buffer")))))

part of Emacs: Xah JS Mode (JavaScript) 📦