[RESOLVED] How to save a Javascript-variable

[MikelSch]

Hello, I would like to save the value of a Javascript-variable into a Visual-Basic-variable. How do I do this?

WebBrowser.Navigate( "javascript: html = document.documentElement.outerHTML; alert(html);" )

[Tom Sawyer]

The simplest way is to create a hidden text box on your webpage with a runat="server" in the tag. In your javascript, set the value of this textbox to the variable and then read the value of that textbox in your code behind.

[stanav]

Tom, I think he is writing a Winform application using the WebBrowser control.

Mike, if you just want the source code of a web page, you can simply have your webbrowser navigate to that url, then read the document.documentElement.outerHTML off your browser in DocumentCompleted event handler.

Dim html As String = WebBrowser1.Document.DocumentElement.OuterHTML

Another way to do is to use Webclient.DownloadString, which is more efficient.

[MikelSch]

@stanav, I really need to read the Javascript-variable. I don't just want the outerHTML. My example may be a little bit confusing.

@Tom Sawyer, but if you want to do so, you have to modify the HTML-code with Javascript and add an additional text box. No?

[Tom Sawyer]

@Tom Sawyer, but if you want to do so, you have to modify the HTML-code and add an additional text box. No?

Yes. It's a hidden textbox, though, so it won't affect the display on the page. If you can't modify the HTML, then all you can do is grab the outerhtml and try to parse through to the variable.

[jmcilhinney]

I don't think it's possible from the outside. I think you'd have to assign an object to the WebBrowser's ObjectForScripting property and then have the JavaScript code assign the value a property of your object. Of course, the Web page would have to be written to support this.

The only other option I can think of would be to use the WebBrowser's DOM, via it's Document property. That means unmanaged code and I'm still not sure it's possible. That would be the place to start researching though.

[MikelSch]

First, thanks for all the answers.

I tried to do it the Tom-Sawyer-Way with a hidden element and it worked just fine (after some hours sitting in front of the computer).

Here's my solution:

Private Function GetVarFromJavaScript(ByVal strJavascript As String, ByVal strJavaScriptVariable As String)
    Dim strNavigation As String = ""
    Dim strReturn As String

    WebBrowser.ScriptErrorsSuppressed = True
    strNavigation &= "javascript:"
    strNavigation &= strJavascript
    strNavigation &= "if(typeof " & strJavaScriptVariable & " == ""undefined"") " & strJavaScriptVariable & " = """";"
    strNavigation &= "if(typeof jsvar == ""undefined""){"
    strNavigation &= "var myElement = document.createElement('<input name=""source"" id=""jsvar"" type=""hidden"" value="""">');"
    strNavigation &= "myElement.value = " & strJavaScriptVariable & ";"
    strNavigation &= "document.body.appendChild(myElement);"
    strNavigation &= "var html = document.documentElement.outerHTML; document.write(html);"
    strNavigation &= "}else{"
    strNavigation &= "document.getElementById(""jsvar"").value = " & strJavaScriptVariable & ";doit();}"
    WebBrowser.Navigate(strNavigation)
    System.Windows.Forms.Application.DoEvents()
    Try
        strReturn = WebBrowser.Document.GetElementById("jsvar").DomElement.Value
    Catch
        strReturn = ""
    End Try
    Return strReturn
End Function

And here's an example how to call the function:

Private Function GetHTML()
    GetVarFromJavaScript("strdomain = document.domain;", "strdomain")
End Sub