Emacs mode to edit JSON

Question

Does anybody know a good Emacs mode to edit JSON? An app I am working on uses a JSON based communication protocol and having the data nicely indented and syntax-highlighted woul

Answer 1

js-mode supports syntax highlighting and indentation for json files.

This is as of Emacs 23.2, when espresso-mode was incorporated into Emacs and renamed js-mode.

Check it out: http://www.nongnu.org/espresso/

Answer 2

Since JSON is a subset of YAML, yaml-mode works too (I don't know how it compares to js-mode and json-mode, though).

Install (from emacs): M-x package-install yaml-mode.

Association of yaml-mode with YAML and JSON files, in ~/.emacs.d/init.el:

(add-to-list 'auto-mode-alist '("\\.yaml$" . yaml-mode))
(add-to-list 'auto-mode-alist '("\\.json$" . yaml-mode))

Answer 3

I've expanded on Mariusz Nowak's workaround, to make it usable as a major mode in its own right. Little modification was required beyond simply deriving the mode; the only change Nowak's work actually needed was the ability to recognize buffers not associated with files, or associated with files whose names don't end in .json, as JSON, which we accomplish with a buffer-local variable.

Here's the augmented workaround:

(make-variable-buffer-local 'js2-parse-as-json)

(defadvice js2-reparse (before json)
    (setq js2-buffer-file-name buffer-file-name))
(ad-activate 'js2-reparse)

(defadvice js2-parse-statement (around json)
    (if (and (= tt js2-LC)
           js2-buffer-file-name
           (or js2-parse-as-json
               (string-equal (substring js2-buffer-file-name -5) ".json"))
           (eq (+ (save-excursion
                    (goto-char (point-min))
                    (back-to-indentation)
                    (while (eolp)
                      (next-line)
                      (back-to-indentation))
                    (point)) 1) js2-ts-cursor))
      (setq ad-return-value (js2-parse-assign-expr))
        ad-do-it))
(ad-activate 'js2-parse-statement)

(define-derived-mode json-mode js2-mode "JSON"
  "Major mode for editing JSON data."
  :group 'json
  (setq js2-parse-as-json t)
  (js2-reparse t))

(add-to-list 'auto-mode-alist '("\\.json$" . json-mode))

If you already use js2-mode, this may be a better option than js-mode plus flymake-json because you need not install anything new (js2-mode already does syntax checking, no need for an external tool), and because this mode will inherit your js2-mode configuration, which js-mode will not.

Answer 4

json.el by Edward O'Connor is part of GNU Emacs since 23.1 (2008).

While it isn't a syntax highlighter, it has a useful function to format JSON:

M-x json-pretty-print-buffer RET

So, if you have a recent version of Emacs, there is no need for jq or python -m json.tool.

Answer 5

+1 for Josh's json-mode -- works well for me. I added

(defun beautify-json ()
  (interactive)
  (let ((b (if mark-active (min (point) (mark)) (point-min)))
        (e (if mark-active (max (point) (mark)) (point-max))))
    (shell-command-on-region b e
     "python -m json.tool" (current-buffer) t)))

and

(define-key json-mode-map (kbd "C-c C-f") 'beautify-json)

to json-mode.el to make the shell command invocation easier.

UPDATE: For those of you with a need/desire to do this with unicode, see my question here. The upshot is rather than using:

python -m json.tool

you will want to use

python -c 'import sys,json; data=json.loads(sys.stdin.read()); print json.dumps(data,sort_keys=True,indent=4).decode("unicode_escape").encode("utf8","replace")'

This both beautifies the JSON as well as preserving the original Unicode content.

Answer 6

I would also recommand js2-mode.

JSON stands for JavaScript Object Notation. It's not another language and it's even not a data container like yaml or xml are. JSON could be used as a data container if there's no function (or in this case we should say method) inside a JSON object, but it's not the primary goal of JSON :-)

var myJSObject = {
  attr: {foo: "bar", baz: ["quux", "truc", "pouet"]},
  fooAlert: function (num) {
    alert(this.attr.foo+' '+num);
  }
};
myJSObject.fooAlert(42);