Type safe Haxe/JSON (de)serializer

cross, json, macro, parsing, position
haxelib install json2object 3.9.0


json2object - Type safe Haxe/JSON (de)serializer

Build Status

This library uses macro and a typed position aware JSON parsing (hxjsonast : https://github.com/nadako/hxjsonast/) to create json parser and writer from and to every supported type.

Incorrect json files or mismatch between the object and the json will yield errors or exceptions, with information on the position of the problematic parts.

Requires at least haxe 3.4.1.


haxelib install json2object


Using the parser

var parser = new json2object.JsonParser<Cls>(); // Creating a parser for Cls class
parser.fromJson(jsonString, filename); // Parsing a string. A filename is specified for errors management
var data:Cls = parser.value; // Access the parsed class
var errors:Array<json2object.Error> = parser.errors; // Access the potential errors yield during the parsing

It is also possible to populate an existing Array with the errors

var errors = new Array<json2object.Error>();
var data:Cls = new json2object.JsonParser<Cls>(errors).fromJson(jsonString, filename);

To print the errors, you can do


Using the writer

var value:Cls;
var writer = new json2object.JsonWriter<Cls>(); // Creating a writer for Cls class
var json = writer.write(value);

The write function accepts an optional String parameter for indenting the json file.

Using the JsonSchema writer

var schema = new json2object.utils.JsonSchemaWriter<Cls>().schema;

The constructor accepts an optional String parameter for indenting the schema. The generated schema follow null-safety rules.

An other parser json2object.utils.special.VSCodeSchemaWriter has been introduced in 3.6.3 to produce a schema with some non standard properties used by VScode.

Constraints in the parsing

  • Variables defined with the @:jignored metadata will be ignored by the parser.
  • Variables defined with the @:optional metadata won't trigger errors if missing.

Supported types

  • Basic types (Int, Float, Bool, String)
  • Null and Array
  • Map with Int or String keys
  • Class (generics are supported)
  • Anonymous structure
  • Typedef alias of supported types
  • Enum values
  • Abstract over a supported type
  • Abstract enum of String, Int, Float or Bool


  • As of version 2.4.0, the parser fields warnings and object have been replaced by errors and value respectively. Since version 3.6.1, previous notations are no longer supported.

  • Anonymous structure variables can be defined to be loaded with a default value if none is specified in the json using the @:default metadata

typedef Struct = {
	var normal:String;

	@:default(new Map<Int, String>())
	var map:Map<Int,String>;

	@:default(-1) @:optional
	var id:Int;
  • @:default(auto) will, by default, initialize each field of the anonymous structure / object to its default value. No effect on non Structure/Object variables.

  • Variable defined as (default, null) may have unexpected behaviour on some extern classes.

  • You can alias a field from the json into another name, for instance if the field name isn't a valid haxe identifier.

typedef Struct = {
	@:alias("public") var isPublic:Bool;
class Main {
	static function main() {
		var parser = new JsonParser<Struct>();
		var data = parser.fromJson('{"public": true }', "file.json");

If multiple alias metadatas are on the variable only the last one is taken into account.

  • As of version 3.4.0, private classes can be parsed except on the CS, Java and HL targets.

  • As of version 3.7.0, it is possible to add field or class specific parser/writer to object using the @:jcustomparse / @:jcustomwrite meta. This increase the type coverage of json parsing/writing. Those custom parser/writer can also be applied to the entire class.

    • The custom writer receive a single parameter, the value to stringify
    • The custom parser receive two parameters: the corresponding json, encoded in a hxjsonast.Json instance, and the name of the field being parsed.
    • The @:jcustom* metadatas require the fully quallified path to the custom function, for instance pack.TheClass.fn or pack.TheModule.TheClass.fn
    • As of version 3.8.0 throwing an exception in a custom parser will be available in parser.errors in the CustomFunctionException member.
class Object {
	public var value:Date;

	public function new() {}

	public static function customWrite(v:Date):String {
		return v.getTime() + '';

	public static function customParse(val:Json, name:String):Date {
		return switch (val.value) {
			case JString(s):
			case JNumber(s):



With an anonymous structure:

import json2object.JsonParser;

class Main {
	static function main() {
		var parser = new JsonParser<{ name : String, quantity : Int }>();
		var data = parser.fromJson('{"name": "computer", "quantity": 2 }', "file.json");
		trace(data.name, data.quantity);

A more complex example with a class and subclass:

import json2object.JsonParser;

class Data {
	public var a:String;
	public var b:SubData;
	public var d:Array<Int>;
	public var e:Array<Map<String, String>>;
	public var f:Array<Float>;
	public var g:Array<Bool>;
	public var h:Math;

class SubData {
	public var c:String;

class Main {
	static function main() {
		var parser = new JsonParser<Data>();
		var data = parser.fromJson('{"a": "a", "b": {"c": "c"}, "e": [ { "c": "1" }, { "c": "2" } ], "f": [], "g": [ true ] }', "file.json");
		var errors = parser.errors;


		for (e in data.e) {


		for (g in data.g) {

		for (e in errors) {
			switch(e) {
				case IncorrectType(variable, expected, pos):
				case UninitializedVariable(variable, pos):
				case UnknownVariable(variable, pos):