With the release of Flash 11 (Oct 2011), Adobe has added native JSON support to Flash, which is significantly faster than anything that can be written in AS3. For projects that want to take advantage of this, while still staying compatible with Flash 9 and 10, there is a new argument in decodeJson and encodeJson that will use the native parser if it is available, giving developers the best of both words.
actionjson includes four projects
decodeJson - A very fast JSON decoder. Around 5-8x faster than as3corelib's JSON decoder
encodeJson - A very fast json encoder. Around 3x faster than as3corelib's JSON encoder
JsonDecoderAsync - An asynchronous JSON parser. Can parse JSON in chunks, making it great for parsing large objects over time. Still around 2x faster than as3corelib's JSON decoder
JsonEncoderAsync - An asynchronous JSON encoder. Encodes JSON in chunks, for large objects that need to be encoded over time. Sadly, about the same speed as as3corelib's JSON encoder
Download the library as a swc here: http://github.com/mherkender/actionjson/raw/master/actionjson.swc