yasnippet for variable number of key-value pairs (concept shamefully stolen from https://github.com/capitaomorte/yasnippet/issues/348)

kv

# -*- mode: snippet -*-
# name: keyvalue
# key: kv
# type: command
# --
(let ((yas-good-grace nil)
      (count (* 2 (read-number "Number of elements: "))))
  (yas-expand-snippet
   (concat "{\n"
           "\t"
           (mapconcat
            #'identity
            (mapcar (lambda (num)
                      (format "${%d:key}: ${%d:value}" num (1+ num)))
                    (number-sequence 1 count 2))
            ",\n")
           "\n"
           "}\n")))