function parseNumber()

in common/lib/jju/parse.js [455:551]
32 lines of code
29 McCabe index (conditional complexity)

  function parseNumber() {
    // rewind because we don't know first char
    position--

    var start = position
      , chr = input[position++]
      , t

    var to_num = function(is_octal) {
      var str = input.substr(start, position - start)

      if (is_octal) {
        var result = parseInt(str.replace(/^0o?/, ''), 8)
      } else {
        var result = Number(str)
      }

      if (Number.isNaN(result)) {
        position--
        fail('Bad numeric literal - "' + input.substr(start, position - start + 1) + '"')
      } else if (!json5 && !str.match(/^-?(0|[1-9][0-9]*)(\.[0-9]+)?(e[+-]?[0-9]+)?$/i)) {
        // additional restrictions imposed by json
        position--
        fail('Non-json numeric literal - "' + input.substr(start, position - start + 1) + '"')
      } else {
        return result
      }
    }

    // ex: -5982475.249875e+29384
    //     ^ skipping this
    if (chr === '-' || (chr === '+' && json5)) chr = input[position++]

    if (chr === 'N' && json5) {
      parseKeyword('NaN')
      return NaN
    }

    if (chr === 'I' && json5) {
      parseKeyword('Infinity')

      // returning +inf or -inf
      return to_num()
    }

    if (chr >= '1' && chr <= '9') {
      // ex: -5982475.249875e+29384
      //        ^^^ skipping these
      while (position < length && isDecDigit(input[position])) position++
      chr = input[position++]
    }

    // special case for leading zero: 0.123456
    if (chr === '0') {
      chr = input[position++]

      //             new syntax, "0o777"           old syntax, "0777"
      var is_octal = chr === 'o' || chr === 'O' || isOctDigit(chr)
      var is_hex = chr === 'x' || chr === 'X'

      if (json5 && (is_octal || is_hex)) {
        while (position < length
           &&  (is_hex ? isHexDigit : isOctDigit)( input[position] )
        ) position++

        var sign = 1
        if (input[start] === '-') {
          sign = -1
          start++
        } else if (input[start] === '+') {
          start++
        }

        return sign * to_num(is_octal)
      }
    }

    if (chr === '.') {
      // ex: -5982475.249875e+29384
      //                ^^^ skipping these
      while (position < length && isDecDigit(input[position])) position++
      chr = input[position++]
    }

    if (chr === 'e' || chr === 'E') {
      chr = input[position++]
      if (chr === '-' || chr === '+') position++
      // ex: -5982475.249875e+29384
      //                       ^^^ skipping these
      while (position < length && isDecDigit(input[position])) position++
      chr = input[position++]
    }

    // we have char in the buffer, so count for it
    position--
    return to_num()
  }