Set of utilities to work with JSON / JSON5 documents.
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jju - a set of utilities to work with JSON / JSON5 documents

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yarn add jju


npm install jju


This module provides following functions:

  1. jju.parse() parses json/json5 text and returns a javascript value it corresponds to
  2. jju.stringify() converts javascript value to an appropriate json/json5 text
  3. jju.tokenize() parses json/json5 text and returns an array of tokens it consists of (see demo)
  4. jju.analyze() parses json/json5 text and tries to guess indentation, quoting style, etc.
  5. jju.update() changes json/json5 text, preserving original formatting as much as possible (see demo)

All functions are able to work with a standard JSON documents. jju.parse() and jju.stringify() are better in some cases, but slower than native JSON.parse() and JSON.stringify() versions. Detailed description see below.

jju.parse() function

 * Main syntax:
 * `text` - text to parse, type: String
 * `options` - parser options, type: Object
jju.parse(text[, options])

// compatibility syntax
jju.parse(text[, reviver])


  • reserved_keys - what to do with reserved keys (String, default="ignore")
    • "ignore" - ignore reserved keys

    • "throw" - throw SyntaxError in case of reserved keys

    • "replace" - replace reserved keys, this is the default JSON.parse behaviour, unsafe

      Reserved keys are keys that exist in an empty object (hasOwnProperty, __proto__, etc.).

// 'ignore' will cause reserved keys to be ignored:
parse('{hasOwnProperty: 1}', {reserved_keys: 'ignore'}) == {}
parse('{hasOwnProperty: 1, x: 2}', {reserved_keys: 'ignore'}).hasOwnProperty('x') == true

// 'throw' will cause SyntaxError in these cases:
parse('{hasOwnProperty: 1}', {reserved_keys: 'throw'}) == SyntaxError

// 'replace' will replace reserved keys with new ones:
parse('{hasOwnProperty: 1}', {reserved_keys: 'replace'}) == {hasOwnProperty: 1}
parse('{hasOwnProperty: 1, x: 2}', {reserved_keys: 'replace'}).hasOwnProperty('x') == TypeError
  • null_prototype - create object as Object.create(null) instead of '{}' (Boolean)

    if reserved_keys != 'replace', default is false

    if reserved_keys == 'replace', default is true

    It is usually unsafe and not recommended to change this option to false in the last case.

  • reviver - reviver function - Function

    This function should follow JSON specification

  • mode - operation mode, set it to 'json' if you want to throw on non-strict json files (String)

jju.stringify() function

 * Main syntax:
 * `value` - value to serialize, type: *
 * `options` - serializer options, type: Object
jju.stringify(value[, options])

// compatibility syntax
jju.stringify(value[, replacer [, indent])


  • ascii - output ascii only (Boolean, default=false) If this option is enabled, output will not have any characters except of 0x20-0x7f.

  • indent - indentation (String, Number or Boolean, default='\t') This option follows JSON specification.

  • quote - enquoting char (String, "'" or '"', default="'")

  • quote_keys - whether keys quoting in objects is required or not (String, default=false) If you want {"q": 1} instead of {q: 1}, set it to true.

  • sort_keys - sort all keys while stringifying (Boolean or Function, default=false) By default sort order will depend on implementation, with v8 it's insertion order. If set to true, all keys (but not arrays) will be sorted alphabetically. You can provide your own sorting function as well.

  • replacer - replacer function or array (Function or Array) This option follows JSON specification.

  • no_trailing_comma = don't output trailing comma (Boolean, default=false) If this option is set, arrays like this [1,2,3,] will never be generated. Otherwise they may be generated for pretty printing.

  • mode - operation mode, set it to 'json' if you want correct json in the output (String)

    Currently it's either 'json' or something else. If it is 'json', following options are implied:

    • options.quote = '"'
    • options.no_trailing_comma = true
    • options.quote_keys = true
    • '\x' literals are not used

jju.tokenize() function

 * Main syntax:
 * `text` - text to tokenize, type: String
 * `options` - parser options, type: Object
jju.tokenize(text[, options])

Options are the same as for the jju.parse function.

Return value is an array of tokens, where each token is an object:

  • raw (String) - raw text of this token, if you join all raw's, you will get the original document
  • type (String) - type of the token, can be whitespace, comment, key, literal, separator or newline
  • stack (Array) - path to the current token in the syntax tree
  • value - value of the token if token is a key or literal

You can check tokenizer for yourself using this demo.

jju.analyze() function

 * Main syntax:
 * `text` - text to analyze, type: String
 * `options` - parser options, type: Object
jju.analyze(text[, options])

Options are the same as for the jju.parse function.

Return value is an object defining a programming style in which the document was written.

  • indent (String) - preferred indentation
  • newline (String) - preferred newline
  • quote (String) - " or ' depending on which quote is preferred
  • quote_keys (Boolean) - true if unquoted keys were used at least once
  • has_whitespace (Boolean) - true if input has a whitespace token
  • has_comments (Boolean) - true if input has a comment token
  • has_newlines (Boolean) - true if input has a newline token
  • has_trailing_comma (Boolean) - true if input has at least one trailing comma

jju.update() function

 * Main syntax:
 * `text` - original text, type: String
 * `new_value` - new value you want to set
 * `options` - parser or stringifier options, type: Object
jju.update(text, new_value[, options])

If you want to update a JSON document, here is the general approach:

// here is your original JSON document:
var input = '{"foo": "bar", "baz": 123}'

// you need to parse it first:
var json = jju.parse(input, {mode: 'json'})
// json is { foo: 'bar', baz: 123 }

// then you can change it as you like: = 'quux'
json.hello = 'world'

// then you run an update function to change the original json:
var output = jju.update(input, json, {mode: 'json'})
// output is '{"foo": "quux", "baz": 123, "hello": "world"}'

Look at this demo to test various types of json.

Advantages over existing JSON libraries

In a few cases it makes sense to use this module instead of built-in JSON methods.


  • better error reporting with source code and line numbers

In case of syntax error, JSON.parse does not return any good information to the user. This module does:

$ node -e 'require("jju").parse("[1,1,1,1,invalid]")'

SyntaxError: Unexpected token 'i' at 0:9

This module is about 5 times slower, so if user experience matters to you more than performance, use this module. If you're working with a lot of machine-generated data, use JSON.parse instead.


  • util.inspect-like pretty printing

This module behaves more smart when dealing with object and arrays, and does not always print newlines in them:

$ node -e 'console.log(require("./").stringify([[,,,],,,[,,,,]], {mode:"json"}))'
        [null, null, null],
        [null, null, null, null]

JSON.stringify will split this into 15 lines, and it's hard to read.

Yet again, this feature comes with a performance hit, so if user experience matters to you more than performance, use this module. If your JSON will be consumed by machines, use JSON.stringify instead.

As a rule of thumb, if you use "space" argument to indent your JSON, you'd better use this module instead.