JSON.stringify replacer that sorts object keys

replacer.coffee

replacer = (key, val) ->
  if val instanceof Object
    keys = Object.keys(val).sort().map (key) ->
      "\"#{key}\":#{JSON.stringify val[key], replacer}"

    "{#{keys}}"
  else val

The following works for me, do you see any potential problems with it? Tested it with deeply nested objects, so far never broke.

replacer = (key, value) ->
  return value unless value.constructor is Object
  Object.keys(value).sort().reduce (sorted, key) ->
    sorted[key] = value[key]
    sorted
  , {}

@ncr, this still relies on order of insertion. try it with {1a: 1, 22: 1} on v8 and you'll get {"22":1,"1a":1}.

@jed the quirk with keys that are parseable as 32bit integers is actually not a problem in my case - I use this code in v8 only, so the key here is not the actual "sorting" but the stability of returned results.

I use this function to ensure that a stringified JSON looks always identical for a given equivalent data so I can sign it.

indeed, assuming v8 doesn't change their iteration implementation. i like the use of reduce too (though not a huge fan of coffee syntax for arguments following functions).

@ncr Thanks, that worked for me, but had to add a null check. In regular JS:

function replacer (key, value) {
  if (value == null || value.constructor != Object) {
    return value
  }
  return Object.keys(value).sort().reduce((s,k) => {s[k] = value[k]; return s}, {})
}