Pack and unpack bytes to strings

I need to write a function that "packs" an array of bytes (integers between 0 and 255) into a string. I also need to be able to perform the reverse operation, to get my byte array from the string that it was packed into. This needs to be done as fast as possible. Seeing as JavaScript has 16-bit strings, I packed two bytes per character. Here is my code and tests: function pack(bytes) { var str = "

[uzulla]

pack/unpack バイナリ操作

[a_bicky]

JavaScript による pack & unpack の実装例