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copied!<p>In simple terms you can't access the length property of a multi-dimensional array in c# via the type dynamic unless, it seems, you have used the length property in JavaScript first...</p> <p>The simple test below shows this very clearly. I hope this saves someone else the head scratching I have been having over the last day or so.</p> <pre><code>[ComVisibleAttribute(true)] public partial class Form1 : Form { public Form1() { InitializeComponent(); webBrowser1.ObjectForScripting = this; StringBuilder html = new StringBuilder(); html.Append("<script>"); html.Append("var arr1 = [1, 2, 3, 4];"); html.Append("var arr2 = [arr1, 2, 3, 4];"); html.Append("var fn1 = function() { return arr1; };"); html.Append("var fn2 = function() { return arr2; };"); html.Append("var fn3 = function() { alert(arr2.length); }"); html.Append("</script>"); webBrowser1.DocumentText = html.ToString(); webBrowser1.DocumentCompleted += (o, e) => { dynamic arr1 = webBrowser1.Document.InvokeScript("fn1"); int i = arr1.length; MessageBox.Show(i.ToString()); //4 // If I call fn3 here then the arr2.length *is* available as int i2 below! ////webBrowser1.Document.InvokeScript("fn3"); // 4 dynamic arr2 = webBrowser1.Document.InvokeScript("fn2"); int i2 = arr2.length; MessageBox.Show(i2.ToString()); // unless fn3 is called you get... /* System.MissingMemberException was unhandled by user code Message=Error while invoking length. Source=System.Dynamic StackTrace: at System.Dynamic.ComRuntimeHelpers.CheckThrowException(Int32 hresult, ExcepInfo& excepInfo, UInt32 argErr, String message) at CallSite.Target(Closure , CallSite , ComObject ) at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0) at CallSite.Target(Closure , CallSite , Object ) at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0) */ }; } } </code></pre> <p><strong>update</strong></p> <p>It seems (see comments) that this behaviour is fixed if the WebBrowser control uses version 9 of Internet Explorer (...the control uses the version of IE on the machine). I can only presume that the IE9 'Chakra' JavaScript engine is doing something extra/different to the old js engine in this case.</p>

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