Add IWebBrowser.CanExecuteJavascriptInMainFrame property, set to true…

…/false when V8Context is created/released

Added checks in the execute/eval javscript methods in WebBrowserExtensions
Made possibly by the addition of OnContextReleased IPC message being added

CefSharp.Core/Internals/ClientAdapter.cpp

@@ -1091,6 +1091,8 @@ namespace CefSharp
                     CefFrameWrapper frameWrapper(browser->GetFrame(GetInt64(argList, 0)));
 
                     handler->OnContextCreated(_browserControl, browserWrapper, %frameWrapper);
+
+                    _browserControl->SetCanExecuteJavascriptOnMainFrame(true);
                 }
 
                 handled = true;
@@ -1105,6 +1107,8 @@ namespace CefSharp
                     CefFrameWrapper frameWrapper(browser->GetFrame(GetInt64(argList, 0)));
 
                     handler->OnContextReleased(_browserControl, browserWrapper, %frameWrapper);
+
+                    _browserControl->SetCanExecuteJavascriptOnMainFrame(false);
                 }
 
                 handled = true;

CefSharp.OffScreen/ChromiumWebBrowser.cs

@@ -282,6 +282,13 @@ public class ChromiumWebBrowser : IRenderWebBrowser
         /// </summary>
         public event EventHandler NewScreenshot;
 
+        /// <summary>
+        /// A flag that indicates if you can execute javascript in the main frame.
+        /// Flag is set to true in IRenderProcessMessageHandler.OnContextCreated.
+        /// and false in IRenderProcessMessageHandler.OnContextReleased
+        /// </summary>
+        public bool CanExecuteJavascriptInMainFrame { get; private set; }
+
         /// <summary>
         /// Top Left position of the popup.
         /// </summary>
@@ -938,6 +945,11 @@ void IWebBrowserInternal.SetTooltipText(string tooltipText)
             TooltipText = tooltipText;
         }
 
+        void IWebBrowserInternal.SetCanExecuteJavascriptOnMainFrame(bool canExecute)
+        {
+            CanExecuteJavascriptInMainFrame = canExecute;
+        }
+
         /// <summary>
         /// Creates a new bitmap with the dimensions of firstBitmap, then
         /// draws the firstBitmap, then overlays the secondBitmap

CefSharp.WinForms/ChromiumWebBrowser.cs

@@ -266,6 +266,14 @@ public class ChromiumWebBrowser : Control, IWebBrowserInternal, IWinFormsWebBrow
         [Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
         public bool IsBrowserInitialized { get; private set; }
 
+        /// <summary>
+        /// A flag that indicates if you can execute javascript in the main frame.
+        /// Flag is set to true in IRenderProcessMessageHandler.OnContextCreated.
+        /// and false in IRenderProcessMessageHandler.OnContextReleased
+        /// </summary>
+        [Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
+        public bool CanExecuteJavascriptInMainFrame { get; private set; }
+
         /// <summary>
         /// Initializes static members of the <see cref="ChromiumWebBrowser"/> class.
         /// </summary>
@@ -664,6 +672,11 @@ void IWebBrowserInternal.OnLoadError(LoadErrorEventArgs args)
             }
         }
 
+        void IWebBrowserInternal.SetCanExecuteJavascriptOnMainFrame(bool canExecute)
+        {
+            CanExecuteJavascriptInMainFrame = canExecute;
+        }
+
         /// <summary>
         /// Gets the browser adapter.
         /// </summary>

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -332,6 +332,13 @@ public class ChromiumWebBrowser : ContentControl, IRenderWebBrowser, IWpfWebBrow
         /// <value>The redo command.</value>
         public ICommand RedoCommand { get; private set; }
 
+        /// <summary>
+        /// A flag that indicates if you can execute javascript in the main frame.
+        /// Flag is set to true in IRenderProcessMessageHandler.OnContextCreated.
+        /// and false in IRenderProcessMessageHandler.OnContextReleased
+        /// </summary>
+        public bool CanExecuteJavascriptInMainFrame { get; private set; }
+
         /// <summary>
         /// Initializes static members of the <see cref="ChromiumWebBrowser"/> class.
         /// </summary>
@@ -861,6 +868,11 @@ void IWebBrowserInternal.OnLoadError(LoadErrorEventArgs args)
             }
         }
 
+        void IWebBrowserInternal.SetCanExecuteJavascriptOnMainFrame(bool canExecute)
+        {
+            CanExecuteJavascriptInMainFrame = canExecute;
+        }
+
         /// <summary>
         /// Gets the browser adapter.
         /// </summary>

CefSharp/IWebBrowser.cs

@@ -237,7 +237,14 @@ public interface IWebBrowser : IDisposable
         string TooltipText { get; }
 
         /// <summary>
-        /// Attempts to give focus to the IWpfWebBrowser control.
+        /// A flag that indicates if you can execute javascript in the main frame.
+        /// Flag is set to true in IRenderProcessMessageHandler.OnContextCreated.
+        /// and false in IRenderProcessMessageHandler.OnContextReleased
+        /// </summary>
+        bool CanExecuteJavascriptInMainFrame { get; }
+
+        /// <summary>
+        /// Attempts to give focus to the IWebBrowser control.
         /// </summary>
         /// <returns><c>true</c> if keyboard focus and logical focus were set to this element; <c>false</c> if only logical focus
         /// was set to this element, or if the call to this method did not force the focus to change.</returns>

CefSharp/Internals/IWebBrowserInternal.cs

@@ -18,6 +18,7 @@ public interface IWebBrowserInternal : IWebBrowser
         void SetLoadingStateChange(LoadingStateChangedEventArgs args);
         void SetTitle(TitleChangedEventArgs args);
         void SetTooltipText(string tooltipText);
+        void SetCanExecuteJavascriptOnMainFrame(bool canExecute);
 
         void OnFrameLoadStart(FrameLoadStartEventArgs args);
         void OnFrameLoadEnd(FrameLoadEndEventArgs args);

CefSharp/WebBrowserExtensions.cs

@@ -207,6 +207,14 @@ public static void ExecuteScriptAsync(this IWebBrowser browser, string methodNam
         /// <param name="script">The Javascript code that should be executed.</param>
         public static void ExecuteScriptAsync(this IWebBrowser browser, string script)
         {
+            if (browser.CanExecuteJavascriptInMainFrame == false)
+            {
+                throw new Exception(@"Unable to execute javascript at this time, scripts can only be executed within a V8Context.
+                                    Use the IWebBrowser.CanExecuteJavascriptInMainFrame property to guard against this exception.
+                                    See https://github.com/cefsharp/CefSharp/wiki/General-Usage#when-can-i-start-executing-javascript
+                                    for more details on when you can execute javascript.");
+            }
+
             using (var frame = browser.GetMainFrame())
             {
                 ThrowExceptionIfFrameNull(frame);
@@ -726,6 +734,14 @@ public static Task<JavascriptResponse> EvaluateScriptAsync(this IWebBrowser brow
                 throw new ArgumentOutOfRangeException("timeout", "Timeout greater than Maximum allowable value of " + UInt32.MaxValue);
             }
 
+            if(browser.CanExecuteJavascriptInMainFrame == false)
+            {
+                throw new Exception(@"Unable to execute javascript at this time, scripts can only be executed within a V8Context.
+                                    Use the IWebBrowser.CanExecuteJavascriptInMainFrame property to guard against this exception.
+                                    See https://github.com/cefsharp/CefSharp/wiki/General-Usage#when-can-i-start-executing-javascript
+                                    for more details on when you can execute javascript.");
+            }
+
             using (var frame = browser.GetMainFrame())
             {
                 ThrowExceptionIfFrameNull(frame);