Stuck converting Javascript function to VB.Net-CodePudding

I need help converting the following JS-function to vb.net please:

function testjs(s) {
    var dict = {};
    var data = (s   "").split("");
    var currChar = data[0];
    var oldPhrase = currChar;
    var out = [currChar];
    var code = 256;
    var phrase;
    for (var i=1; i<data.length; i  ) {
        var currCode = data[i].charCodeAt(0);
        if (currCode < 256) {
            phrase = data[i];
        }
        else {
           phrase = dict[currCode] ? dict[currCode] : (oldPhrase   currChar);
        }
        out.push(phrase);
        currChar = phrase.charAt(0);
        dict[code] = oldPhrase   currChar;
        code  ;
        oldPhrase = phrase;
    }
    return out.join("");
}

What my code looks like at the moment:

Private Function questionmarkop(ByVal ph As String, ByVal dictatcurr As String, ByVal ophoc As String) As String
    Return If(ph = dictatcurr, dictatcurr, ophoc)
End Function


Private Function testvb(ByVal s As String) As String
        Dim dict As New Dictionary(Of Integer, String)
        Dim data As Char() = s.ToCharArray
        Dim currchar As Char = data(0)
        Dim oldphrase As String = currchar
        Dim out As String() = {currchar}
        Dim code As Integer = 256
        Dim phrase As String = ""
        Dim ret As String = ""
        For i As Integer = 1 To data.Length - 1
            Dim currcode As Integer = Convert.ToInt16(data(i))
            If currcode < 256 Then
                phrase = data(i)
            Else
                phrase = questionmarkop(phrase, dict(currcode), (oldphrase   currchar))
            End If
            ReDim Preserve out(out.Length)
            out(out.Length - 1) = phrase
            currchar = phrase(0)
            dict.Item(code) = oldphrase   currchar
            code  = 1
            oldphrase = phrase
        Next
        For Each str As String In out
            ret = ret   str
        Next
        Return ret
    End Function

When inputting the following string s: thisĂaveryshorttestđringtogiĆanexamplefČđackoĆrflow

The function should return: thisisaveryshortteststringtogiveanexampleforstackoverflow

The js function does exactly that, my vb function does not sadly. The first time (or basically everytime) the if statement is not true, the next character will be wrong. So i figure there is something wrong with the line phrase = questionmarkop(phrase, dict(currcode), (oldphrase currchar)). With the test string i provided everything works until this, after that i have the first false char. Can someone help me figure out what i am doing wrong here?

CodePudding user response：

Based on discussion in the comments, it seems like the issue was producing a VB translation for this line:

phrase = dict[currCode] ? dict[currCode] : (oldPhrase   currChar);

I have only passing familiarity with Javascript, but I believe the key here is that dict[currCode] will return a type of null or missing value if there is not already an entry in the dictionary with key currCode. The .NET dictionary has facilities that will let you get the same effect, though the exact implementation is a little different.

The direct VB equivalent to this ternary and assignment is (I believe):

phrase = If(dict.ContainsKey(currCode), dict(currCode), oldPhrase & currChar)

You can eliminate a key lookup on the dictionary by using Dictionary.TryGetValue:

If Not dict.TryGetValue(currCode, phrase) Then
    phrase = oldPhrase & currChar
End If

I doubt the code is performance-sensitive enough to care about the difference, so I would recommend to use the alternative that you find more clear to read.