JsonMap.hx

package ;

abstract JsonMap<T>({ }) from {} {
	public function new() this = {};
	public function exists(key:String) return Reflect.hasField(this, key);
	@:arrayAccess public function get(key:String) return Reflect.field(this, key);
	@:arrayAccess public function set(key:String, value:T):T {
		Reflect.setField(this, key, value);
		return value;
	}
	public function keys():Array<String> return Reflect.fields(this);
	public function remove(key:String) return Reflect.deleteField(this, key);
	public function iterator():Iterator<T> {
		var i = 0,
			keys = keys();
		return {
			hasNext : function () return i < keys.length,
			next: function () return get(this, keys[i++])
		}
	}
}

Usage.hx

package ;

class Usage {
	static function main() {
		var obj: { h : JsonMap<String> } = haxe.Json.parse('{ "h": { "key1" : "value1" } }');
		trace(obj.h.exists('key1'));//true
		trace(obj.h.exists('key2'));//false
		trace(obj.h['key1']);//value1
	}
}