JSON Encode string literal "asdf\\nsedfgs" - json

Question

I am working with an old classic asp/vbscript app that has a json class.
I have a string literal: asdf\\nsedfgs e.g. thats not escaped json or anything. its literally those characters.
So, to use that value in a JSON string, it should be something like this, right?
{"somedesc":"asdf\\\\nsedfgs"}
...with the two backslash characters escaped.
However, on the way out of JSON and back to string literal, we'd do something like this (in this order)
val = Replace(val, "\""", """")
val = Replace(val, "\\", "\")
val = Replace(val, "\/", "/")
val = Replace(val, "\b", Chr(8))
val = Replace(val, "\f", Chr(12))
val = Replace(val, "\n", Chr(10))
val = Replace(val, "\r", Chr(13))
val = Replace(val, "\t", Chr(9))
...but for the string above, this sequence of replace() gives us the incorrect decoded value:
result (note the newline, as the 4 \ got replaced to two, then the \n got replaced to a newline)
asdf\
sedfgs
So questions:
how does one encode and decode a literal asdf\\nsedfgs to and from json correctly?
is that decode logic correct? in the correct order? It seems not, because how could it distinguish between a literal \n vs an escaped chr(13)?
is there something else I am missing here?

Answer 1

The important part is isolating the escaped backslashes from the rest of the string so that they don't interfere with escape sequences- You can split the string, reattach the missing parts later:
Const ENCODE = FALSE
Const DECODE = TRUE
val = "asdf\\\\nsedfgs"
val = JSON(val, DECODE)
MsgBox val
'Swap replacement values & dividers + concatenation characters
val = JSON(val, ENCODE)
MsgBox val
Function JSON(ByVal str, ByVal mode)
Dim key, val
Set d = CreateObject("Scripting.Dictionary")
d.Add "\/", "/"
d.Add "\b", Chr(8)
d.Add "\f", Chr(12)
d.Add "\n", Chr(10)
d.Add "\r", Chr(13)
d.Add "\t", Chr(9)
If mode Then
d.Add "\""", """"
d.Add "\\", "\"
div = "\\"
cat = "\"
key = d.Keys
val = d.Items
Else
d.Add "\\", "\"
d.Add "\""", """"
div = "\"
cat = "\\"
key = d.Items
val = d.Keys
End If
arr = Split(str, div)
For i = 0 To UBound(arr)
For j = 0 To UBound(key)
arr(i) = Replace(arr(i), key(j), val(j))
Next
output = output & arr(i)
If i <> UBound(arr) Then output = output & cat
Next
d.RemoveAll
JSON = output
End Function