Own realization SAX parser of JSON

JSON2.coffee

JSON2 =
  OBJECT:"Object"
  ARRAY:"Array"
  nextToken: (buf,i)->
    token = undefined
    isWord = false
    isNum = false
    isFloat = false
    str = ""
    while i < buf.length
      ch = buf.charCodeAt(i)
      ++i
      switch ch
        when 123, 125, 58, 91, 93, 44 #'{' '}' ':' '[' ']' ','
          return [String.fromCharCode(ch),str,i]
        when 34 #"
          isWord = not isWord
          unless isWord then return ["w",str,i]
        else
          if ch is 46 and isNum #.
            unless isFloat
              isFloat = true
            else
              throw new Error("more then one char '.' in number token")
          if not isWord and ch >= 48 and ch <= 57 #[0..9]
            isNum = true

          if isWord or isNum
            str += String.fromCharCode(ch)

          if isNum and i + 1 < buf.length
            ch = buf.charCodeAt(i+1)
            if (ch < 48 or ch > 57) and ch != 46
              return \
                unless isFloat
                  ['i',parseInt(str),i]
                else
                  ["f",parseFloat(str),i]
    ["","",i]
  processValue: (obj,key,value,type)->
    if type is @OBJECT
      if key? and value? and obj?
        obj[key] = value
      else
        throw new Error("Invalid params for [#{type}]: key:'#{key}' value:'#{value}' obj:'#{obj}'")

    else if type is @ARRAY
      if value? and obj?
        obj.push value
      else
        throw new Error("Invalid params for [#{type}]: value:'#{value}' obj:'#{obj}'")
    else
      throw new Error("Unknown type")
    key = null
    value = null
    [obj,key,value,type]
  _parse: (buf,obj,i, type)->
    key = null
    value = null
    try
      while i < buf.length
        [token,v,i] = @nextToken(buf,i)
        switch token
          when "{"
            [i,value] = @_parse(buf,{},i,@OBJECT)
          when "["
            [i,value] = @_parse(buf,[],i, @ARRAY)
          when "}","]"
            [obj,key,value,type] = @processValue(obj,key,value,type)
            return [i,obj]
          when ","
            [obj,key,value,type] = @processValue(obj,key,value,type)
          when ":"
            key = value
            value = null
          when "w", "i", "f"
            value = v
    catch e
      e.buf = buf
      e.i = i
      throw e
    [i,value]
  parse: (buf)->
    try
      @_parse(buf,{},0,@OBJECT)[1]
    catch e
      throw new Error("msg:#{e.message} text:#{e.buf.slice(0,e.i).to}")

DATA = """
{
  "one":[0,"1",0,"3","4","9"],
  "two":"three",
  "four":{
    1:"one",
    "five":1.0,
    "six":3
  }
}
"""
res = JSON2.parse DATA.toString()
if res.one.length == 6 then console.log("PASS") else console.error("FAIL")
if res.one[0] == 0 then console.log("PASS") else console.error("FAIL")
if res.one[1] == "1" then console.log("PASS") else console.error("FAIL")
if res.two == "three" then console.log("PASS") else console.error("FAIL")
if res.four["1"]=="one" then console.log("PASS") else console.error("FAIL")