Read Javascript variable from Web Browser control

Question

I am trying to read the value of a Javascript variable which is loaded and called from a WebBrowser control on my form.

Example:

index.html refers to a javas

Answer 1

You can use IHTMLDocument::Script to retrieve the automation interface of the script engine. If you use the Windows Forms webbrowser control in C#, this means casting the HtmlDocument.DomDocument property to mshtml.IHTMLDocument. For WPF you cast the document directly.

Global variables are added to the script engine as properties and global functions as methods. Until IE9, you can use the IDispatch interface to access those functions/variables if you know their names. HtmlDocument.InvokeScript and WPF's WebBrowser.InvokeScript wraps this up in a nice way, but only for System.Reflection.BindingFlags.InvokeMethod. For accessing variables you need to pass DISPATCH_PROPERTYGET when you call Invoke, that is, use BindingFlags.GetProperty in managed code.

Manual late binding is not fun, In case you want to know how laborious late binding is, check Binding for Office automation servers with Visual C# .NET.

There is a problem in IE9 that the variables/functions are not accessible via IDispatch, but you can still access variables/functions via IDispatchEx in a similar way.