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JSON 3 is a modern JSON implementation compatible with a variety of JavaScript platforms, including Internet Explorer 6, Opera 7, Safari 2, and Netscape 6. The current version is 3.2.6.

CDN copies are also available at cdnjs & jsDelivr.

JSON is a language-independent data interchange format based on a loose subset of the JavaScript grammar. Originally popularized by Douglas Crockford, the format was standardized in the fifth edition of the ECMAScript specification. The 5.1 edition, ratified in June 2011, incorporates several modifications to the grammar pertaining to the serialization of dates.

JSON 3 exposes two functions: stringify() for serializing a JavaScript value to JSON, and parse() for producing a JavaScript value from a JSON source string. It is a drop-in replacement for JSON 2. The functions behave exactly as described in the ECMAScript spec, except for the date serialization discrepancy noted below.

The JSON 3 parser does not use eval or regular expressions. This provides security and performance benefits in obsolete and mobile environments, where the margin is particularly significant. The complete benchmark suite is available on jsPerf.

The project is hosted on GitHub, along with the unit tests. It is part of the BestieJS family, a collection of best-in-class JavaScript libraries that promote cross-platform support, specification precedents, unit testing, and plenty of documentation.

Changes from JSON 2


  • Correctly serializes primitive wrapper objects.
  • Throws a TypeError when serializing cyclic structures (JSON 2 recurses until the call stack overflows).
  • Utilizes feature tests to detect broken or incomplete native JSON implementations (JSON 2 only checks for the presence of the native functions). The tests are only executed once at runtime, so there is no additional performance cost when parsing or serializing values.

As of v3.2.3, JSON 3 is compatible with Prototype 1.6.1 and older.

In contrast to JSON 2, JSON 3 does not

  • Add toJSON() methods to the Boolean, Number, and String prototypes. These are not part of any standard, and are made redundant by the design of the stringify() implementation.
  • Add toJSON() or toISOString() methods to Date.prototype. See the note about date serialization below.

Date Serialization

JSON 3 deviates from the specification in one important way: it does not define Date#toISOString() or Date#toJSON(). This preserves CommonJS compatibility and avoids polluting native prototypes. Instead, date serialization is performed internally by the stringify() implementation: if a date object does not define a custom toJSON() method, it is serialized as a simplified ISO 8601 date-time string.

Several native Date#toJSON() implementations produce date time strings that do not conform to the grammar outlined in the spec. For instance, all versions of Safari 4, as well as JSON 2, fail to serialize extended years correctly. Furthermore, JSON 2 and older implementations omit the milliseconds from the date-time string (optional in ES 5, but required in 5.1). Finally, in all versions of Safari 4 and 5, serializing an invalid date will produce the string "Invalid Date", rather than null. Because these environments exhibit other serialization bugs, however, JSON 3 will override the native stringify() implementation.

Portions of the date serialization code are adapted from the date-shim project.


Web Browsers

<script src="http://bestiejs.github.io/json3/lib/json3.js"></script>
  JSON.stringify({"Hello": 123});
  // => '{"Hello":123}'
  JSON.parse("[[1, 2, 3], 1, 2, 3, 4]", function (key, value) {
    if (typeof value == "number") {
      value = value % 2 ? "Odd" : "Even";
    return value;
  // => [["Odd", "Even", "Odd"], "Odd", "Even", "Odd", "Even"]

CommonJS Environments

var JSON3 = require("./path/to/json3");
JSON3.parse("[1, 2, 3]");
// => [1, 2, 3]

JavaScript Engines

JSON.stringify({"Hello": 123, "Good-bye": 456}, ["Hello"], "\t");
// => '{\n\t"Hello": 123\n}'


JSON 3 has been tested with the following web browsers, CommonJS environments, and JavaScript engines.

Web Browsers

CommonJS Environments

JavaScript Engines

  • Mozilla Rhino 1.5R5 and higher
  • WebKit JSC
  • Google V8

Known Incompatibilities

  • Attempting to serialize the arguments object may produce inconsistent results across environments due to specification version differences. As a workaround, please convert the arguments object to an array first: JSON.stringify([].slice.call(arguments, 0)).

Required Native Methods

JSON 3 assumes that the following methods exist and function as described in the ECMAScript specification:

  • The Number, String, Array, Object, Date, SyntaxError, and TypeError constructors.
  • String.fromCharCode
  • Object#toString
  • Function#call
  • Math.floor
  • Number#toString
  • Date#valueOf
  • String.prototype: indexOf, charCodeAt, charAt, slice.
  • Array.prototype: push, pop, join.


Check out a working copy of the JSON 3 source code with Git:

$ git clone git://github.com/bestiejs/json3.git
$ cd json3
$ git submodule update --init

If you’d like to contribute a feature or bug fix, you can fork JSON 3, commit your changes, and send a pull request. Please make sure to update the unit tests in the test directory as well.

Alternatively, you can use the GitHub issue tracker to submit bug reports, feature requests, and questions, or send tweets to @kitcambridge.

JSON 3 is released under the MIT License.