Introducing json.el (original) (raw)

JSON is a lightweight data interchange format based on a subset of JavaScript. You can read all about JSON at json.org.json.el is a JSON parser and generator for Emacs Lisp, which can produce an Emacs Lisp data structure from a JSON object and vice-versa. It’s been Included with Emacs since February 2008.

Using it is pretty straightforward; here are some examples.

• (require 'json) json

JSON's primitive values are strings, numbers, and the keywordstrue, false, and null.

• (json-read-from-string "true") t
• (json-encode t) "true"
• (json-read-from-string "4.5") 4.5
• (json-read-from-string "\\"foo\\"") "foo"

JSON's compound values are arrays and dictionaries.

• (json-read-from-string "[true, 4.5]") [t 4.5]
• (json-read-from-string "{\\"foo\\": true}") ((foo . t))

Notice that we read the JSON array as a lisp vector and the JSON dictionary as an alist. We could just have read the array as a list, and the dictionary as a plist or hashtable. json.el allows for all of these representations. (Also, note that the alist keys are symbols; we could read these as keywords or strings.)

• dictionary-as-plist:
• (let ((json-object-type 'plist)) (json-read-from-string "{\\"foo\\": true}")) (:foo t)
• key-as-string:
• (let ((json-key-type 'string)) (json-read-from-string "{\\"foo\\": true}")) (("foo" . t))
• dictionary-as-hashtable:
• `(let ((json-object-type 'hash-table))
  (json-read-from-string "{\"foo\": true}"))

#<hash-table 'equal nil 1/65 0x314f800>

• (gethash "foo" *)
  t`

json.el generally does the right thing when encoding idiomatic lisp data structures:

• (json-encode '(1 2 3)) "[1, 2, 3]"
• (json-encode '(:foo 1 :bar 2 :baz 3)) "{\\"foo\\":1, \\"bar\\":2, \\"baz\\":3}"