Low-level MonoSanity tests for invoking JS from .NET code

samples/MonoSanity/wwwroot/index.html

@@ -28,7 +28,7 @@
   </fieldset>
 
   <fieldset>
-    <legend>Trigger exception</legend>
+    <legend>Trigger .NET exception</legend>
     <form id="triggerException">
       <input id="triggerExceptionMessage" value="Your message here" />
       <button type="submit" disabled>Go</button>
@@ -36,6 +36,15 @@
     </form>
   </fieldset>
 
+  <fieldset>
+    <legend>Call JS from .NET</legend>
+    <form id="callJs">
+      <input id="callJsEvalExpression" value="location.href" />
+      <button type="submit" disabled>Go</button>
+      <div><textarea rows="5" cols="80" readonly id="callJsResult"></textarea></div>
+    </form>
+  </fieldset>
+
   <p id="loadingIndicator">Loading...</p>
 
   <script src="loader.js"></script>
@@ -54,7 +63,7 @@
       var b = parseInt(el('addNumberB').value);
       var result = invokeMonoMethod('MonoSanityClient', 'MonoSanityClient', 'Examples', 'AddNumbers', [a, b]);
       el('addNumbersResult').value = result;
-    }
+    };
 
     el('repeatString').onsubmit = function (evt) {
       evt.preventDefault();
@@ -62,7 +71,7 @@
       var count = parseInt(el('repeatStringCount').value);
       var result = invokeMonoMethod('MonoSanityClient', 'MonoSanityClient', 'Examples', 'RepeatString', [str, count]);
       el('repeatStringResult').value = result;
-    }
+    };
 
     el('triggerException').onsubmit = function (evt) {
       evt.preventDefault();
@@ -73,11 +82,28 @@
       } catch (ex) {
         el('triggerExceptionMessageStackTrace').value = ex.toString();
       }
-    }
+    };
+
+    el('callJs').onsubmit = function (evt) {
+      evt.preventDefault();
+      var expression = el('callJsEvalExpression').value;
+      var result = invokeMonoMethod('MonoSanityClient', 'MonoSanityClient', 'Examples', 'EvaluateJavaScript', [expression]);
+      el('callJsResult').value = result;
+    };
 
     function el(id) {
       return document.getElementById(id);
     }
+
+    // Examples of functions we can invoke from .NET
+
+    function getUserAgentString() {
+      return navigator.userAgent;
+    }
+
+    function triggerJsException() {
+      throw new Error('This is a JavaScript exception.');
+    }
   </script>
 </body>
 </html>

samples/MonoSanityClient/Examples.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Text;
+using WebAssembly;
 
 namespace MonoSanityClient
 {
@@ -27,5 +28,16 @@ namespace MonoSanityClient
         {
             throw new InvalidOperationException(message);
         }
+
+        public static string EvaluateJavaScript(string expression)
+        {
+            var result = Runtime.InvokeJS(expression, out var resultIsException);
+            if (resultIsException != 0)
+            {
+                return $".NET got exception: {result}";
+            }
+
+            return $".NET received: {result}";
+        }
     }
 }

samples/MonoSanityClient/WebAssembly.Runtime.cs

@@ -0,0 +1,15 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Runtime.CompilerServices;
+
+namespace WebAssembly
+{
+    internal static class Runtime
+    {
+        // The exact namespace, type, and method name must match the corresponding entry in
+        // driver.c in the Mono distribution
+        [MethodImpl(MethodImplOptions.InternalCall)]
+        public static extern string InvokeJS(string str, out int resultIsException);
+    }
+}

test/Microsoft.Blazor.E2ETest/Tests/MonoSanityTest.cs

@@ -4,6 +4,7 @@
 using Microsoft.Blazor.E2ETest.Infrastructure;
 using Microsoft.Blazor.E2ETest.Infrastructure.ServerFixtures;
 using OpenQA.Selenium;
+using System;
 using Xunit;
 
 namespace Microsoft.Blazor.E2ETest.Tests
@@ -48,7 +49,7 @@ namespace Microsoft.Blazor.E2ETest.Tests
         }
 
         [Fact]
-        public void CanTriggerException()
+        public void CanReceiveDotNetExceptionInJavaScript()
         {
             Navigate("/", noReload: true);
 
@@ -58,6 +59,26 @@ namespace Microsoft.Blazor.E2ETest.Tests
             Assert.Contains("Hello from test", GetValue(Browser, "triggerExceptionMessageStackTrace"));
         }
 
+        [Fact]
+        public void CanCallJavaScriptFromDotNet()
+        {
+            Navigate("/", noReload: true);
+            SetValue(Browser, "callJsEvalExpression", "getUserAgentString()");
+            Browser.FindElement(By.CssSelector("#callJs button")).Click();
+            var result = GetValue(Browser, "callJsResult");
+            Assert.StartsWith(".NET received: Mozilla", result);
+        }
+
+        [Fact]
+        public void CanReceiveJavaScriptExceptionInDotNet()
+        {
+            Navigate("/", noReload: true);
+            SetValue(Browser, "callJsEvalExpression", "triggerJsException()");
+            Browser.FindElement(By.CssSelector("#callJs button")).Click();
+            var result = GetValue(Browser, "callJsResult");
+            Assert.StartsWith(".NET got exception: Error: This is a JavaScript exception.", result);
+        }
+
         private static string GetValue(IWebDriver webDriver, string elementId)
         {
             var element = webDriver.FindElement(By.Id(elementId));