Defer link interception until Router is initialized (#10062)

* Defer link interception until Router is initialized

Fixes https://github.com/aspnet/AspNetCore/issues/9834

src/Components/Blazor/Blazor/ref/Microsoft.AspNetCore.Blazor.netstandard2.0.cs

@@ -76,7 +76,7 @@ namespace Microsoft.AspNetCore.Blazor.Services
         protected override void EnsureInitialized() { }
         protected override void NavigateToCore(string uri, bool forceLoad) { }
         [Microsoft.JSInterop.JSInvokableAttribute("NotifyLocationChanged")]
-        public static void NotifyLocationChanged(string newAbsoluteUri) { }
+        public static void NotifyLocationChanged(string newAbsoluteUri, bool isInterceptedLink) { }
     }
 }
 namespace Microsoft.AspNetCore.Components.Builder

src/Components/Blazor/Blazor/src/Hosting/WebAssemblyHostBuilder.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Net.Http;
 using Microsoft.AspNetCore.Blazor.Services;
 using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Routing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.JSInterop;
 
@@ -90,6 +91,7 @@ namespace Microsoft.AspNetCore.Blazor.Hosting
             services.AddSingleton<IJSRuntime>(WebAssemblyJSRuntime.Instance);
             services.AddSingleton<IComponentContext, WebAssemblyComponentContext>();
             services.AddSingleton<IUriHelper>(WebAssemblyUriHelper.Instance);
+            services.AddSingleton<INavigationInterception>(WebAssemblyNavigationInterception.Instance);
             services.AddSingleton<HttpClient>(s =>
             {
                 // Creating the URI helper needs to wait until the JS Runtime is initialized, so defer it.

src/Components/Blazor/Blazor/src/Services/WebAssemblyNavigationInterception.cs

@@ -0,0 +1,20 @@
+// 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.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Routing;
+using Interop = Microsoft.AspNetCore.Components.Browser.BrowserUriHelperInterop;
+
+namespace Microsoft.AspNetCore.Blazor.Services
+{
+    internal sealed class WebAssemblyNavigationInterception : INavigationInterception
+    {
+        public static readonly WebAssemblyNavigationInterception Instance = new WebAssemblyNavigationInterception();
+
+        public Task EnableNavigationInterceptionAsync()
+        {
+            WebAssemblyJSRuntime.Instance.Invoke<object>(Interop.EnableNavigationInterception);
+            return Task.CompletedTask;
+        }
+    }
+}

src/Components/Blazor/Blazor/src/Services/WebAssemblyUriHelper.cs

@@ -28,7 +28,7 @@ namespace Microsoft.AspNetCore.Blazor.Services
         protected override void EnsureInitialized()
         {
             WebAssemblyJSRuntime.Instance.Invoke<object>(
-                Interop.EnableNavigationInterception,
+                Interop.ListenForNavigationEvents,
                 typeof(WebAssemblyUriHelper).Assembly.GetName().Name,
                 nameof(NotifyLocationChanged));
 
@@ -54,10 +54,10 @@ namespace Microsoft.AspNetCore.Blazor.Services
         /// For framework use only.
         /// </summary>
         [JSInvokable(nameof(NotifyLocationChanged))]
-        public static void NotifyLocationChanged(string newAbsoluteUri)
+        public static void NotifyLocationChanged(string newAbsoluteUri, bool isInterceptedLink)
         {
             Instance.SetAbsoluteUri(newAbsoluteUri);
-            Instance.TriggerOnLocationChanged();
+            Instance.TriggerOnLocationChanged(isInterceptedLink);
         }
 
         /// <summary>

src/Components/Browser.JS/dist/Debug/blazor.server.js

@@ -14885,62 +14885,76 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 };
 Object.defineProperty(exports, "__esModule", { value: true });
 __webpack_require__(/*! @dotnet/jsinterop */ "../node_modules/@dotnet/jsinterop/dist/Microsoft.JSInterop.js");
-var hasRegisteredEventListeners = false;
+var hasRegisteredNavigationInterception = false;
+var hasRegisteredNavigationEventListeners = false;
 // Will be initialized once someone registers
 var notifyLocationChangedCallback = null;
 // These are the functions we're making available for invocation from .NET
 exports.internalFunctions = {
+    listenForNavigationEvents: listenForNavigationEvents,
     enableNavigationInterception: enableNavigationInterception,
     navigateTo: navigateTo,
     getBaseURI: function () { return document.baseURI; },
     getLocationHref: function () { return location.href; },
 };
-function enableNavigationInterception(assemblyName, functionName) {
+function listenForNavigationEvents(assemblyName, functionName) {
-    if (hasRegisteredEventListeners || assemblyName === undefined || functionName === undefined) {
+    if (hasRegisteredNavigationEventListeners) {
         return;
     }
     notifyLocationChangedCallback = { assemblyName: assemblyName, functionName: functionName };
-    hasRegisteredEventListeners = true;
+    hasRegisteredNavigationEventListeners = true;
+    window.addEventListener('popstate', function () { return notifyLocationChanged(false); });
+}
+function enableNavigationInterception() {
+    if (hasRegisteredNavigationInterception) {
+        return;
+    }
+    hasRegisteredNavigationInterception = true;
     document.addEventListener('click', function (event) {
+        if (event.button !== 0 || eventHasSpecialKey(event)) {
+            // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows
+            return;
+        }
         // Intercept clicks on all <a> elements where the href is within the <base href> URI space
         // We must explicitly check if it has an 'href' attribute, because if it doesn't, the result might be null or an empty string depending on the browser
         var anchorTarget = findClosestAncestor(event.target, 'A');
         var hrefAttributeName = 'href';
-        if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName) && event.button === 0) {
+        if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName)) {
-            var href = anchorTarget.getAttribute(hrefAttributeName);
-            var absoluteHref = toAbsoluteUri(href);
             var targetAttributeValue = anchorTarget.getAttribute('target');
             var opensInSameFrame = !targetAttributeValue || targetAttributeValue === '_self';
-            // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows
+            if (!opensInSameFrame) {
-            if (isWithinBaseUriSpace(absoluteHref) && !eventHasSpecialKey(event) && opensInSameFrame) {
+                return;
+            }
+            var href = anchorTarget.getAttribute(hrefAttributeName);
+            var absoluteHref = toAbsoluteUri(href);
+            if (isWithinBaseUriSpace(absoluteHref)) {
                 event.preventDefault();
-                performInternalNavigation(absoluteHref);
+                performInternalNavigation(absoluteHref, true);
             }
         }
     });
-    window.addEventListener('popstate', handleInternalNavigation);
 }
 function navigateTo(uri, forceLoad) {
     var absoluteUri = toAbsoluteUri(uri);
     if (!forceLoad && isWithinBaseUriSpace(absoluteUri)) {
-        performInternalNavigation(absoluteUri);
+        performInternalNavigation(absoluteUri, false);
     }
     else {
         location.href = uri;
     }
 }
 exports.navigateTo = navigateTo;
-function performInternalNavigation(absoluteInternalHref) {
+function performInternalNavigation(absoluteInternalHref, interceptedLink) {
     history.pushState(null, /* ignored title */ '', absoluteInternalHref);
-    handleInternalNavigation();
+    notifyLocationChanged(interceptedLink);
 }
-function handleInternalNavigation() {
+function notifyLocationChanged(interceptedLink) {
     return __awaiter(this, void 0, void 0, function () {
         return __generator(this, function (_a) {
             switch (_a.label) {
                 case 0:
                     if (!notifyLocationChangedCallback) return [3 /*break*/, 2];
-                    return [4 /*yield*/, DotNet.invokeMethodAsync(notifyLocationChangedCallback.assemblyName, notifyLocationChangedCallback.functionName, location.href)];
+                    return [4 /*yield*/, DotNet.invokeMethodAsync(notifyLocationChangedCallback.assemblyName, notifyLocationChangedCallback.functionName, location.href, interceptedLink)];
                 case 1:
                     _a.sent();
                     _a.label = 2;

src/Components/Browser.JS/dist/Debug/blazor.webassembly.js

@@ -2450,62 +2450,76 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 };
 Object.defineProperty(exports, "__esModule", { value: true });
 __webpack_require__(/*! @dotnet/jsinterop */ "../node_modules/@dotnet/jsinterop/dist/Microsoft.JSInterop.js");
-var hasRegisteredEventListeners = false;
+var hasRegisteredNavigationInterception = false;
+var hasRegisteredNavigationEventListeners = false;
 // Will be initialized once someone registers
 var notifyLocationChangedCallback = null;
 // These are the functions we're making available for invocation from .NET
 exports.internalFunctions = {
+    listenForNavigationEvents: listenForNavigationEvents,
     enableNavigationInterception: enableNavigationInterception,
     navigateTo: navigateTo,
     getBaseURI: function () { return document.baseURI; },
     getLocationHref: function () { return location.href; },
 };
-function enableNavigationInterception(assemblyName, functionName) {
+function listenForNavigationEvents(assemblyName, functionName) {
-    if (hasRegisteredEventListeners || assemblyName === undefined || functionName === undefined) {
+    if (hasRegisteredNavigationEventListeners) {
         return;
     }
     notifyLocationChangedCallback = { assemblyName: assemblyName, functionName: functionName };
-    hasRegisteredEventListeners = true;
+    hasRegisteredNavigationEventListeners = true;
+    window.addEventListener('popstate', function () { return notifyLocationChanged(false); });
+}
+function enableNavigationInterception() {
+    if (hasRegisteredNavigationInterception) {
+        return;
+    }
+    hasRegisteredNavigationInterception = true;
     document.addEventListener('click', function (event) {
+        if (event.button !== 0 || eventHasSpecialKey(event)) {
+            // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows
+            return;
+        }
         // Intercept clicks on all <a> elements where the href is within the <base href> URI space
         // We must explicitly check if it has an 'href' attribute, because if it doesn't, the result might be null or an empty string depending on the browser
         var anchorTarget = findClosestAncestor(event.target, 'A');
         var hrefAttributeName = 'href';
-        if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName) && event.button === 0) {
+        if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName)) {
-            var href = anchorTarget.getAttribute(hrefAttributeName);
-            var absoluteHref = toAbsoluteUri(href);
             var targetAttributeValue = anchorTarget.getAttribute('target');
             var opensInSameFrame = !targetAttributeValue || targetAttributeValue === '_self';
-            // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows
+            if (!opensInSameFrame) {
-            if (isWithinBaseUriSpace(absoluteHref) && !eventHasSpecialKey(event) && opensInSameFrame) {
+                return;
+            }
+            var href = anchorTarget.getAttribute(hrefAttributeName);
+            var absoluteHref = toAbsoluteUri(href);
+            if (isWithinBaseUriSpace(absoluteHref)) {
                 event.preventDefault();
-                performInternalNavigation(absoluteHref);
+                performInternalNavigation(absoluteHref, true);
             }
         }
     });
-    window.addEventListener('popstate', handleInternalNavigation);
 }
 function navigateTo(uri, forceLoad) {
     var absoluteUri = toAbsoluteUri(uri);
     if (!forceLoad && isWithinBaseUriSpace(absoluteUri)) {
-        performInternalNavigation(absoluteUri);
+        performInternalNavigation(absoluteUri, false);
     }
     else {
         location.href = uri;
     }
 }
 exports.navigateTo = navigateTo;
-function performInternalNavigation(absoluteInternalHref) {
+function performInternalNavigation(absoluteInternalHref, interceptedLink) {
     history.pushState(null, /* ignored title */ '', absoluteInternalHref);
-    handleInternalNavigation();
+    notifyLocationChanged(interceptedLink);
 }
-function handleInternalNavigation() {
+function notifyLocationChanged(interceptedLink) {
     return __awaiter(this, void 0, void 0, function () {
         return __generator(this, function (_a) {
             switch (_a.label) {
                 case 0:
                     if (!notifyLocationChangedCallback) return [3 /*break*/, 2];
-                    return [4 /*yield*/, DotNet.invokeMethodAsync(notifyLocationChangedCallback.assemblyName, notifyLocationChangedCallback.functionName, location.href)];
+                    return [4 /*yield*/, DotNet.invokeMethodAsync(notifyLocationChangedCallback.assemblyName, notifyLocationChangedCallback.functionName, location.href, interceptedLink)];
                 case 1:
                     _a.sent();
                     _a.label = 2;

src/Components/Browser.JS/package.json

@@ -5,6 +5,7 @@
   "description": "",
   "main": "index.js",
   "scripts": {
+    "build": "yarn run build:debug && yarn run build:production",
     "build:debug": "cd src && webpack --mode development --config ./webpack.config.js",
     "build:production": "cd src && webpack --mode production --config ./webpack.config.js",
     "test": "jest"

src/Components/Browser.JS/src/Services/UriHelper.ts

@@ -1,69 +1,88 @@
 import '@dotnet/jsinterop';
 
-let hasRegisteredEventListeners = false;
+let hasRegisteredNavigationInterception = false;
+let hasRegisteredNavigationEventListeners = false;
 
 // Will be initialized once someone registers
 let notifyLocationChangedCallback: { assemblyName: string; functionName: string } | null = null;
 
 // These are the functions we're making available for invocation from .NET
 export const internalFunctions = {
+  listenForNavigationEvents,
   enableNavigationInterception,
   navigateTo,
   getBaseURI: () => document.baseURI,
   getLocationHref: () => location.href,
 };
 
-function enableNavigationInterception(assemblyName: string, functionName: string) {
+function listenForNavigationEvents(assemblyName: string, functionName: string) {
-  if (hasRegisteredEventListeners || assemblyName === undefined || functionName === undefined) {
+  if (hasRegisteredNavigationEventListeners) {
     return;
   }
 
   notifyLocationChangedCallback = { assemblyName, functionName };
-  hasRegisteredEventListeners = true;
+
+  hasRegisteredNavigationEventListeners = true;
+  window.addEventListener('popstate', () => notifyLocationChanged(false));
+}
+
+function enableNavigationInterception() {
+  if (hasRegisteredNavigationInterception) {
+    return;
+  }
+
+  hasRegisteredNavigationInterception = true;
 
   document.addEventListener('click', event => {
+    if (event.button !== 0 || eventHasSpecialKey(event)) {
+      // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows
+      return;
+    }
+
     // Intercept clicks on all <a> elements where the href is within the <base href> URI space
     // We must explicitly check if it has an 'href' attribute, because if it doesn't, the result might be null or an empty string depending on the browser
     const anchorTarget = findClosestAncestor(event.target as Element | null, 'A') as HTMLAnchorElement;
     const hrefAttributeName = 'href';
-    if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName) && event.button === 0) {
+    if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName)) {
-      const href = anchorTarget.getAttribute(hrefAttributeName)!;
-      const absoluteHref = toAbsoluteUri(href);
       const targetAttributeValue = anchorTarget.getAttribute('target');
       const opensInSameFrame = !targetAttributeValue || targetAttributeValue === '_self';
+      if (!opensInSameFrame) {
+        return;
+      }
 
-      // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows
+      const href = anchorTarget.getAttribute(hrefAttributeName)!;
-      if (isWithinBaseUriSpace(absoluteHref) && !eventHasSpecialKey(event) && opensInSameFrame) {
+      const absoluteHref = toAbsoluteUri(href);
+
+      if (isWithinBaseUriSpace(absoluteHref)) {
         event.preventDefault();
-        performInternalNavigation(absoluteHref);
+        performInternalNavigation(absoluteHref, true);
       }
     }
   });
-
-  window.addEventListener('popstate', handleInternalNavigation);
 }
 
 export function navigateTo(uri: string, forceLoad: boolean) {
   const absoluteUri = toAbsoluteUri(uri);
 
   if (!forceLoad && isWithinBaseUriSpace(absoluteUri)) {
-    performInternalNavigation(absoluteUri);
+    performInternalNavigation(absoluteUri, false);
   } else {
     location.href = uri;
   }
 }
 
-function performInternalNavigation(absoluteInternalHref: string) {
+function performInternalNavigation(absoluteInternalHref: string, interceptedLink: boolean) {
   history.pushState(null, /* ignored title */ '', absoluteInternalHref);
-  handleInternalNavigation();
+  notifyLocationChanged(interceptedLink);
 }
 
-async function handleInternalNavigation() {
+async function notifyLocationChanged(interceptedLink: boolean) {
   if (notifyLocationChangedCallback) {
     await DotNet.invokeMethodAsync(
       notifyLocationChangedCallback.assemblyName,
       notifyLocationChangedCallback.functionName,
-      location.href
+      location.href,
+      interceptedLink
     );
   }
 }

src/Components/Browser/src/BrowserUriHelperInterop.cs

@@ -8,6 +8,8 @@ namespace Microsoft.AspNetCore.Components.Browser
     {
         private static readonly string Prefix = "Blazor._internal.uriHelper.";
 
+        public static readonly string ListenForNavigationEvents = Prefix + "listenForNavigationEvents";
+
         public static readonly string EnableNavigationInterception = Prefix + "enableNavigationInterception";
 
         public static readonly string GetLocationHref = Prefix + "getLocationHref";

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -367,7 +367,7 @@ namespace Microsoft.AspNetCore.Components
     }
     public partial interface IUriHelper
     {
-        event System.EventHandler<string> OnLocationChanged;
+        event System.EventHandler<Microsoft.AspNetCore.Components.Routing.LocationChangedEventArgs> OnLocationChanged;
         string GetAbsoluteUri();
         string GetBaseUri();
         void NavigateTo(string uri);
@@ -599,7 +599,7 @@ namespace Microsoft.AspNetCore.Components
     public abstract partial class UriHelperBase : Microsoft.AspNetCore.Components.IUriHelper
     {
         protected UriHelperBase() { }
-        public event System.EventHandler<string> OnLocationChanged { add { } remove { } }
+        public event System.EventHandler<Microsoft.AspNetCore.Components.Routing.LocationChangedEventArgs> OnLocationChanged { add { } remove { } }
         protected virtual void EnsureInitialized() { }
         public string GetAbsoluteUri() { throw null; }
         public virtual string GetBaseUri() { throw null; }
@@ -611,7 +611,7 @@ namespace Microsoft.AspNetCore.Components
         protected void SetAbsoluteUri(string uri) { }
         public System.Uri ToAbsoluteUri(string href) { throw null; }
         public string ToBaseRelativePath(string baseUri, string locationAbsolute) { throw null; }
-        protected void TriggerOnLocationChanged() { }
+        protected void TriggerOnLocationChanged(bool isinterceptedLink) { }
     }
 }
 namespace Microsoft.AspNetCore.Components.Forms
@@ -849,6 +849,19 @@ namespace Microsoft.AspNetCore.Components.RenderTree
 }
 namespace Microsoft.AspNetCore.Components.Routing
 {
+    public partial interface INavigationInterception
+    {
+        System.Threading.Tasks.Task EnableNavigationInterceptionAsync();
+    }
+    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
+    public readonly partial struct LocationChangedEventArgs
+    {
+        private readonly object _dummy;
+        private readonly int _dummyPrimitive;
+        public LocationChangedEventArgs(string location, bool isNavigationIntercepted) { throw null; }
+        public bool IsNavigationIntercepted { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        public string Location { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+    }
     public enum NavLinkMatch
     {
         Prefix = 0,

src/Components/Components/src/IUriHelper.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using Microsoft.AspNetCore.Components.Routing;
 
 namespace Microsoft.AspNetCore.Components
 {
@@ -19,7 +20,7 @@ namespace Microsoft.AspNetCore.Components
         /// <summary>
         /// An event that fires when the navigation location has changed.
         /// </summary>
-        event EventHandler<string> OnLocationChanged;
+        event EventHandler<LocationChangedEventArgs> OnLocationChanged;
 
         /// <summary>
         /// Converts a relative URI into an absolute one (by resolving it

src/Components/Components/src/Microsoft.AspNetCore.Components.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk.Razor">
+<Project Sdk="Microsoft.NET.Sdk.Razor">
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>

src/Components/Components/src/Routing/INavigationInterception.cs

@@ -0,0 +1,19 @@
+// 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.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Components.Routing
+{
+    /// <summary>
+    /// Contract to setup navigation interception on the client.
+    /// </summary>
+    public interface INavigationInterception
+    {
+        /// <summary>
+        /// Enables navigation interception on the client.
+        /// </summary>
+        /// <returns>A <see cref="Task" /> that represents the asynchronous operation.</returns>
+        Task EnableNavigationInterceptionAsync();
+    }
+}

src/Components/Components/src/Routing/LocationChangedEventArgs.cs

@@ -0,0 +1,34 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Components.Routing
+{
+    /// <summary>
+    /// <see cref="EventArgs" /> for <see cref="IUriHelper.OnLocationChanged" />.
+    /// </summary>
+    public readonly struct LocationChangedEventArgs
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="LocationChangedEventArgs" />.
+        /// </summary>
+        /// <param name="location">The location.</param>
+        /// <param name="isNavigationIntercepted">A value that determines if navigation for the link was intercepted.</param>
+        public LocationChangedEventArgs(string location, bool isNavigationIntercepted)
+        {
+            Location = location;
+            IsNavigationIntercepted = isNavigationIntercepted;
+        }
+
+        /// <summary>
+        /// Gets the changed location.
+        /// </summary>
+        public string Location { get; }
+
+        /// <summary>
+        /// Gets a value that determines if navigation for the link was intercepted.
+        /// </summary>
+        public bool IsNavigationIntercepted { get; }
+    }
+}

src/Components/Components/src/Routing/NavLink.cs

@@ -1,12 +1,11 @@
 // 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 Microsoft.AspNetCore.Components;
-using Microsoft.AspNetCore.Components.RenderTree;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.RenderTree;
 
 namespace Microsoft.AspNetCore.Components.Routing
 {
@@ -83,11 +82,11 @@ namespace Microsoft.AspNetCore.Components.Routing
             UriHelper.OnLocationChanged -= OnLocationChanged;
         }
 
-        private void OnLocationChanged(object sender, string newUriAbsolute)
+        private void OnLocationChanged(object sender, LocationChangedEventArgs args)
         {
             // We could just re-render always, but for this component we know the
             // only relevant state change is to the _isActive property.
-            var shouldBeActiveNow = ShouldMatch(newUriAbsolute);
+            var shouldBeActiveNow = ShouldMatch(args.Location);
             if (shouldBeActiveNow != _isActive)
             {
                 _isActive = shouldBeActiveNow;

src/Components/Components/src/Routing/Router.cs

@@ -14,16 +14,21 @@ namespace Microsoft.AspNetCore.Components.Routing
     /// A component that displays whichever other component corresponds to the
     /// current navigation location.
     /// </summary>
-    public class Router : IComponent, IDisposable
+    public class Router : IComponent, IHandleAfterRender, IDisposable
     {
         static readonly char[] _queryOrHashStartChar = new[] { '?', '#' };
 
         RenderHandle _renderHandle;
         string _baseUri;
         string _locationAbsolute;
+        bool _navigationInterceptionEnabled;
 
         [Inject] private IUriHelper UriHelper { get; set; }
 
+        [Inject] private INavigationInterception NavigationInterception { get; set; }
+
+        [Inject] private IComponentContext ComponentContext { get; set; }
+
         /// <summary>
         /// Gets or sets the assembly that should be searched, along with its referenced
         /// assemblies, for components matching the URI.
@@ -33,7 +38,7 @@ namespace Microsoft.AspNetCore.Components.Routing
         /// <summary>
         /// Gets or sets the type of the component that should be used as a fallback when no match is found for the requested route.
         /// </summary>
-        [Parameter] public Type FallbackComponent { get; private set; }
+        [Parameter] public RenderFragment NotFoundContent { get; private set; }
 
         private RouteTable Routes { get; set; }
 
@@ -52,7 +57,7 @@ namespace Microsoft.AspNetCore.Components.Routing
             parameters.SetParameterProperties(this);
             var types = ComponentResolver.ResolveComponents(AppAssembly);
             Routes = RouteTable.Create(types);
-            Refresh();
+            Refresh(isNavigationIntercepted: false);
             return Task.CompletedTask;
         }
 
@@ -79,41 +84,57 @@ namespace Microsoft.AspNetCore.Components.Routing
             builder.CloseComponent();
         }
 
-        private void Refresh()
+        private void Refresh(bool isNavigationIntercepted)
         {
             var locationPath = UriHelper.ToBaseRelativePath(_baseUri, _locationAbsolute);
             locationPath = StringUntilAny(locationPath, _queryOrHashStartChar);
             var context = new RouteContext(locationPath);
             Routes.Route(context);
 
-            if (context.Handler == null)
+            if (context.Handler != null)
             {
-                if (FallbackComponent != null)
+                if (!typeof(IComponent).IsAssignableFrom(context.Handler))
                 {
-                    context.Handler = FallbackComponent;
+                    throw new InvalidOperationException($"The type {context.Handler.FullName} " +
+                        $"does not implement {typeof(IComponent).FullName}.");
+                }
+
+                _renderHandle.Render(builder => Render(builder, context.Handler, context.Parameters));
+            }
+            else
+            {
+                if (!isNavigationIntercepted && NotFoundContent != null)
+                {
+                    // We did not find a Component that matches the route.
+                    // Only show the NotFoundContent if the application developer programatically got us here i.e we did not
+                    // intercept the navigation. In all other cases, force a browser navigation since this could be non-Blazor content.
+                    _renderHandle.Render(NotFoundContent);
                 }
                 else
                 {
-                    throw new InvalidOperationException($"'{nameof(Router)}' cannot find any component with a route for '/{locationPath}', and no fallback is defined.");
+                    UriHelper.NavigateTo(_locationAbsolute, forceLoad: true);
                 }
             }
-
-            if (!typeof(IComponent).IsAssignableFrom(context.Handler))
-            {
-                throw new InvalidOperationException($"The type {context.Handler.FullName} " +
-                    $"does not implement {typeof(IComponent).FullName}.");
-            }
-
-            _renderHandle.Render(builder => Render(builder, context.Handler, context.Parameters));
         }
 
-        private void OnLocationChanged(object sender, string newAbsoluteUri)
+        private void OnLocationChanged(object sender, LocationChangedEventArgs args)
         {
-            _locationAbsolute = newAbsoluteUri;
+            _locationAbsolute = args.Location;
-            if (_renderHandle.IsInitialized)
+            if (_renderHandle.IsInitialized && Routes != null)
             {
-                Refresh();
+                Refresh(args.IsNavigationIntercepted);
             }
         }
+
+        Task IHandleAfterRender.OnAfterRenderAsync()
+        {
+            if (!_navigationInterceptionEnabled && ComponentContext.IsConnected)
+            {
+                _navigationInterceptionEnabled = true;
+                return NavigationInterception.EnableNavigationInterceptionAsync();
+            }
+
+            return Task.CompletedTask;
+        }
     }
 }

src/Components/Components/src/UriHelperBase.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using Microsoft.AspNetCore.Components.Routing;
 
 namespace Microsoft.AspNetCore.Components
 {
@@ -10,12 +11,12 @@ namespace Microsoft.AspNetCore.Components
     /// </summary>
     public abstract class UriHelperBase : IUriHelper
     {
-        private EventHandler<string> _onLocationChanged;
+        private EventHandler<LocationChangedEventArgs> _onLocationChanged;
 
         /// <summary>
         /// An event that fires when the navigation location has changed.
         /// </summary>
-        public event EventHandler<string> OnLocationChanged
+        public event EventHandler<LocationChangedEventArgs> OnLocationChanged
         {
             add
             {
@@ -205,9 +206,9 @@ namespace Microsoft.AspNetCore.Components
         /// <summary>
         /// Triggers the <see cref="OnLocationChanged"/> event with the current URI value.
         /// </summary>
-        protected void TriggerOnLocationChanged()
+        protected void TriggerOnLocationChanged(bool isinterceptedLink)
         {
-            _onLocationChanged?.Invoke(this, _uri);
+            _onLocationChanged?.Invoke(this, new LocationChangedEventArgs(_uri, isinterceptedLink));
         }
 
         private void AssertInitialized()

src/Components/ComponentsNoDeps.slnf

@@ -29,7 +29,7 @@
       "test\\testassets\\ComponentsApp.App\\ComponentsApp.App.csproj",
       "test\\testassets\\ComponentsApp.Server\\ComponentsApp.Server.csproj",
       "test\\testassets\\TestContentPackage\\TestContentPackage.csproj",
-      "test\\testassets\\TestServer\\TestServer.csproj"
+      "test\\testassets\\TestServer\\Components.TestServer.csproj"
     ]
   }
 }

src/Components/Server/ref/Microsoft.AspNetCore.Components.Server.netcoreapp3.0.cs

@@ -83,7 +83,7 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
         public override void InitializeState(string uriAbsolute, string baseUriAbsolute) { }
         protected override void NavigateToCore(string uri, bool forceLoad) { }
         [Microsoft.JSInterop.JSInvokableAttribute("NotifyLocationChanged")]
-        public static void NotifyLocationChanged(string uriAbsolute) { }
+        public static void NotifyLocationChanged(string uriAbsolute, bool isInterceptedLink) { }
     }
 }
 namespace Microsoft.Extensions.DependencyInjection

src/Components/Server/src/Circuits/CircuitHost.cs

@@ -8,6 +8,7 @@ using System.Threading.Tasks;
 using Microsoft.AspNetCore.Components.Browser;
 using Microsoft.AspNetCore.Components.Browser.Rendering;
 using Microsoft.AspNetCore.Components.Rendering;
+using Microsoft.AspNetCore.Components.Routing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using Microsoft.JSInterop;
@@ -120,6 +121,12 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
                 {
                     uriHelper.AttachJsRuntime(JSRuntime);
                 }
+
+                var navigationInterception = (RemoteNavigationInterception)Services.GetRequiredService<INavigationInterception>();
+                if (!navigationInterception.HasAttachedJSRuntime)
+                {
+                    navigationInterception.AttachJSRuntime(JSRuntime);
+                }
             }
         }
 

src/Components/Server/src/Circuits/DefaultCircuitFactory.cs

@@ -8,6 +8,7 @@ using System.Text.Encodings.Web;
 using Microsoft.AspNetCore.Components.Browser;
 using Microsoft.AspNetCore.Components.Browser.Rendering;
 using Microsoft.AspNetCore.Components.Rendering;
+using Microsoft.AspNetCore.Components.Routing;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
 using Microsoft.Extensions.DependencyInjection;
@@ -49,12 +50,15 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
             (authenticationStateProvider as FixedAuthenticationStateProvider)?.Initialize(httpContext.User);
 
             var uriHelper = (RemoteUriHelper)scope.ServiceProvider.GetRequiredService<IUriHelper>();
+            var navigationInterception = (RemoteNavigationInterception)scope.ServiceProvider.GetRequiredService<INavigationInterception>();
             if (client.Connected)
             {
                 uriHelper.AttachJsRuntime(jsRuntime);
                 uriHelper.InitializeState(
                     uriAbsolute,
                     baseUriAbsolute);
+
+                navigationInterception.AttachJSRuntime(jsRuntime);
             }
             else
             {

src/Components/Server/src/Circuits/RemoteNavigationInterception.cs

@@ -0,0 +1,43 @@
+// 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;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Routing;
+using Microsoft.JSInterop;
+using Interop = Microsoft.AspNetCore.Components.Browser.BrowserUriHelperInterop;
+
+namespace Microsoft.AspNetCore.Components.Server.Circuits
+{
+    internal sealed class RemoteNavigationInterception : INavigationInterception
+    {
+        private IJSRuntime _jsRuntime;
+
+        public void AttachJSRuntime(IJSRuntime jsRuntime)
+        {
+            if (HasAttachedJSRuntime)
+            {
+                throw new InvalidOperationException("JSRuntime has already been initialized.");
+            }
+
+            _jsRuntime = jsRuntime;
+        }
+
+        public bool HasAttachedJSRuntime => _jsRuntime != null;
+
+        public async Task EnableNavigationInterceptionAsync()
+        {
+            if (!HasAttachedJSRuntime)
+            {
+                // We should generally never get here in the ordinary case. Router will only call this API once pre-rendering is complete.
+                // This would guard any unusual usage of this API.
+                throw new InvalidOperationException("Navigation commands can not be issued at this time. This is because the component is being " +
+                    "prerendered and the page has not yet loaded in the browser or because the circuit is currently disconnected. " +
+                    "Components must wrap any navigation calls in conditional logic to ensure those navigation calls are not " +
+                    "attempted during prerendering or while the client is disconnected.");
+            }
+
+            await _jsRuntime.InvokeAsync<object>(Interop.EnableNavigationInterception);
+        }
+    }
+}

src/Components/Server/src/Circuits/RemoteUriHelper.cs

@@ -14,8 +14,8 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
     /// </summary>
     public class RemoteUriHelper : UriHelperBase
     {
-        private IJSRuntime _jsRuntime;
         private readonly ILogger<RemoteUriHelper> _logger;
+        private IJSRuntime _jsRuntime;
 
         /// <summary>
         /// Creates a new <see cref="RemoteUriHelper"/> instance.
@@ -39,7 +39,7 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
         public override void InitializeState(string uriAbsolute, string baseUriAbsolute)
         {
             base.InitializeState(uriAbsolute, baseUriAbsolute);
-            TriggerOnLocationChanged();
+            TriggerOnLocationChanged(isinterceptedLink: false);
         }
 
         /// <summary>
@@ -52,11 +52,13 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
             {
                 throw new InvalidOperationException("JavaScript runtime already initialized.");
             }
+
             _jsRuntime = jsRuntime;
+
             _jsRuntime.InvokeAsync<object>(
-                    Interop.EnableNavigationInterception,
+                Interop.ListenForNavigationEvents,
-                    typeof(RemoteUriHelper).Assembly.GetName().Name,
+                typeof(RemoteUriHelper).Assembly.GetName().Name,
-                    nameof(NotifyLocationChanged));
+                nameof(NotifyLocationChanged));
 
             _logger.LogDebug($"{nameof(RemoteUriHelper)} initialized.");
         }
@@ -65,7 +67,7 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
         /// For framework use only.
         /// </summary>
         [JSInvokable(nameof(NotifyLocationChanged))]
-        public static void NotifyLocationChanged(string uriAbsolute)
+        public static void NotifyLocationChanged(string uriAbsolute, bool isInterceptedLink)
         {
             var circuit = CircuitHost.Current;
             if (circuit == null)
@@ -73,19 +75,18 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
                 var message = $"{nameof(NotifyLocationChanged)} called without a circuit.";
                 throw new InvalidOperationException(message);
             }
-
             var uriHelper = (RemoteUriHelper)circuit.Services.GetRequiredService<IUriHelper>();
 
             uriHelper.SetAbsoluteUri(uriAbsolute);
 
             uriHelper._logger.LogDebug($"Location changed to '{uriAbsolute}'.");
-            uriHelper.TriggerOnLocationChanged();
+            uriHelper.TriggerOnLocationChanged(isInterceptedLink);
         }
 
         /// <inheritdoc />
         protected override void NavigateToCore(string uri, bool forceLoad)
         {
-            _logger.LogDebug($"Log debug {uri} force load {forceLoad}.");
+            _logger.LogDebug($"{uri} force load {forceLoad}.");
 
             if (_jsRuntime == null)
             {

src/Components/Server/src/DependencyInjection/ComponentServiceCollectionExtensions.cs

@@ -3,6 +3,7 @@
 
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Routing;
 using Microsoft.AspNetCore.Components.Server;
 using Microsoft.AspNetCore.Components.Server.BlazorPack;
 using Microsoft.AspNetCore.Components.Server.Circuits;
@@ -66,6 +67,7 @@ namespace Microsoft.Extensions.DependencyInjection
             // These intentionally replace the non-interactive versions included in MVC.
             services.AddScoped<IUriHelper, RemoteUriHelper>();
             services.AddScoped<IJSRuntime, RemoteJSRuntime>();
+            services.AddScoped<INavigationInterception, RemoteNavigationInterception>();
             services.AddScoped<IComponentContext, RemoteComponentContext>();
             services.AddScoped<AuthenticationStateProvider, FixedAuthenticationStateProvider>();
 

src/Components/test/E2ETest/ServerExecutionTests/ServerSideAppTest.cs

@@ -2,8 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections;
-using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
@@ -206,6 +204,5 @@ window.Blazor._internal.forceCloseConnection();");
             Browser.True(() => Browser.Manage().Logs.GetLog(LogType.Browser)
                 .Any(l => l.Level == LogLevel.Info && l.Message.Contains("Connection disconnected.")));
         }
-
     }
 }

src/Components/test/E2ETest/Tests/RoutingTest.cs

@@ -291,6 +291,16 @@ namespace Microsoft.AspNetCore.Components.E2ETest.Tests
             AssertHighlightedLinks("Default with hash");
         }
 
+        [Fact]
+        public void CanFollowLinkToNotAComponent()
+        {
+            SetUrlViaPushState("/");
+
+            var app = MountTestComponent<TestRouter>();
+            app.FindElement(By.LinkText("Not a component")).Click();
+            Browser.Equal("Not a component!", () => Browser.FindElement(By.Id("test-info")).Text);
+        }
+
         [Fact]
         public void CanNavigateProgrammatically()
         {
@@ -339,12 +349,30 @@ namespace Microsoft.AspNetCore.Components.E2ETest.Tests
             AssertHighlightedLinks("Default (matches all)", "Default with base-relative URL (matches all)");
         }
 
-        private void SetUrlViaPushState(string relativeUri)
+        [Fact]
+        public void UsingUriHelperWithoutRouterWorks()
+        {
+            var app = MountTestComponent<UriHelperComponent>();
+            var initialUrl = Browser.Url;
+
+            Browser.Equal(Browser.Url, () => app.FindElement(By.Id("test-info")).Text);
+            var uri = SetUrlViaPushState("/mytestpath");
+            Browser.Equal(uri, () => app.FindElement(By.Id("test-info")).Text);
+
+            var jsExecutor = (IJavaScriptExecutor)Browser;
+            jsExecutor.ExecuteScript("history.back()");
+
+            Browser.Equal(initialUrl, () => app.FindElement(By.Id("test-info")).Text);
+        }
+
+        private string SetUrlViaPushState(string relativeUri)
         {
             var pathBaseWithoutHash = ServerPathBase.Split('#')[0];
             var jsExecutor = (IJavaScriptExecutor)Browser;
             var absoluteUri = new Uri(_serverFixture.RootUri, $"{pathBaseWithoutHash}{relativeUri}");
             jsExecutor.ExecuteScript($"Blazor.navigateTo('{absoluteUri.ToString().Replace("'", "\\'")}')");
+
+            return absoluteUri.AbsoluteUri;
         }
 
         private void AssertHighlightedLinks(params string[] linkTexts)

src/Components/test/testassets/BasicTestApp/Index.razor

@@ -37,6 +37,7 @@
         <option value="BasicTestApp.EventBubblingComponent">Event bubbling</option>
         <option value="BasicTestApp.EventPreventDefaultComponent">Event preventDefault</option>
         <option value="BasicTestApp.RouterTest.TestRouter">Router</option>
+        <option value="BasicTestApp.RouterTest.TestRouterWithoutNotFoundContent">Router without NotFoundContent</option>
         <option value="BasicTestApp.HtmlBlockChildContent">ChildContent HTML Block</option>
         <option value="BasicTestApp.HtmlMixedChildContent">ChildContent Mixed Block</option>
         <option value="BasicTestApp.HtmlEncodedChildContent">ChildContent HTML Encoded Block</option>
@@ -52,6 +53,7 @@
         <option value="BasicTestApp.InteropOnInitializationComponent">Interop on initialization</option>
         <option value="BasicTestApp.KeyCasesComponent">Key cases</option>
         <option value="BasicTestApp.ReorderingFocusComponent">Reordering focus retention</option>
+        <option value="BasicTestApp.RouterTest.UriHelperComponent">UriHelper Test</option>
     </select>
 
   @if (SelectedComponentType != null)

src/Components/test/testassets/BasicTestApp/RouterTest/Error404.razor

@@ -1 +0,0 @@
-<div id="test-info">Oops, that component wasn't found!</div>

src/Components/test/testassets/BasicTestApp/RouterTest/Links.razor

@@ -27,3 +27,6 @@
 </a>
 
 <a href="/" target="_blank">Target (_blank)</a>
+
+<a href="/subdir/NotAComponent.html">Not a component</a>
+

src/Components/test/testassets/BasicTestApp/RouterTest/TestRouter.razor

@@ -1,2 +1,6 @@
 @using Microsoft.AspNetCore.Components.Routing
-<Router AppAssembly=typeof(BasicTestApp.Program).Assembly FallbackComponent="typeof(Error404)" />
+<Router AppAssembly=typeof(BasicTestApp.Program).Assembly>
+    <NotFoundContent>
+        <div id="test-info">Oops, that component wasn't found!</div>
+    </NotFoundContent>
+</Router>

src/Components/test/testassets/BasicTestApp/RouterTest/UriHelperComponent.razor

@@ -0,0 +1,27 @@
+@inject IUriHelper UriHelper
+@inject Microsoft.JSInterop.IJSRuntime JSRuntime
+
+<button onclick="@Navigate">Navigate</button>
+
+<span id="test-info">@UrlLocation</span>
+
+@functions{
+    string UrlLocation;
+
+    protected override void OnInit()
+    {
+        base.OnInit();
+        UrlLocation = UriHelper.GetAbsoluteUri();
+        UriHelper.OnLocationChanged += (_, __) =>
+        {
+            UrlLocation = UriHelper.GetAbsoluteUri();
+            StateHasChanged();
+        };
+    }
+
+    async Task Navigate()
+    {
+        await JSRuntime.InvokeAsync<object>("uriHelperNavigate");
+    }
+}
+

src/Components/test/testassets/BasicTestApp/wwwroot/NotAComponent.html

@@ -0,0 +1 @@
+<div id="test-info">Not a component!</div>

src/Components/test/testassets/BasicTestApp/wwwroot/index.html

@@ -19,6 +19,10 @@
       return element.value;
     }
 
+    function uriHelperNavigate() {
+      Blazor.navigateTo('/subdir/some-path');
+    }
+
     (function () {
       // Load either blazor.webassembly.js or blazor.server.js depending
       // on the hash part of the URL. This is just to give a way for the

src/Components/test/testassets/ComponentsApp.App/Shared/NavMenu.razor

@@ -37,6 +37,11 @@
                 <span class="oi oi-list-rich" aria-hidden="true"></span> Error
             </NavLink>
         </li>
+        <li class="nav-item px-3">
+            <NavLink class="nav-link" href="links">
+                <span class="oi oi-list-rich" aria-hidden="true"></span> Links
+            </NavLink>
+        </li>
     </ul>
 </div>
 

src/Components/test/testassets/ComponentsApp.Server/Pages/Index.cshtml

@@ -1,4 +1,4 @@
-@page
+@page
 @using ComponentsApp.App
 
 <!DOCTYPE html>
@@ -12,8 +12,7 @@
     <link href="css/site.css" rel="stylesheet" />
 </head>
 <body>
-
+    <app>@(await Html.RenderComponentAsync<App>(new { Name = "Guest" }))</app>
-    <app>@(await Html.RenderComponentAsync<App>(new { Name="Guest" }))</app>
 
     <script src="_framework/blazor.server.js" autostart="false"></script>
     <script>

src/Components/test/testassets/TestServer/Startup.cs

@@ -2,6 +2,7 @@ using BasicTestApp;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Components.Server;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;

src/Mvc/Mvc.ViewFeatures/src/DependencyInjection/MvcViewFeaturesMvcCoreBuilderExtensions.cs

@@ -5,6 +5,7 @@ using System;
 using System.Buffers;
 using System.Linq;
 using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Routing;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.ApplicationModels;
 using Microsoft.AspNetCore.Mvc.ApplicationParts;
@@ -207,6 +208,8 @@ namespace Microsoft.Extensions.DependencyInjection
             services.TryAddScoped<StaticComponentRenderer>();
             services.TryAddScoped<IUriHelper, HttpUriHelper>();
             services.TryAddScoped<IJSRuntime, UnsupportedJavaScriptRuntime>();
+            services.TryAddScoped<IComponentContext, UnsupportedComponentContext>();
+            services.TryAddScoped<INavigationInterception, UnsupportedNavigationInterception>();
 
             services.TryAddTransient<ControllerSaveTempDataPropertyFilter>();
 

src/Mvc/Mvc.ViewFeatures/src/Infrastructure/HttpUriHelper.cs

@@ -3,8 +3,6 @@
 
 using System;
 using Microsoft.AspNetCore.Components;
-using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Http.Extensions;
 
 namespace Microsoft.AspNetCore.Mvc.ViewFeatures
 {

src/Mvc/Mvc.ViewFeatures/src/RazorComponents/UnsupportedComponentContext.cs

@@ -0,0 +1,12 @@
+// 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 Microsoft.AspNetCore.Components;
+
+namespace Microsoft.AspNetCore.Mvc.ViewFeatures
+{
+    internal class UnsupportedComponentContext : IComponentContext
+    {
+        public bool IsConnected => false;
+    }
+}

src/Mvc/Mvc.ViewFeatures/src/RazorComponents/UnsupportedNavigationInterception.cs

@@ -0,0 +1,18 @@
+// 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;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Routing;
+
+namespace Microsoft.AspNetCore.Mvc.ViewFeatures
+{
+    internal sealed class UnsupportedNavigationInterception : INavigationInterception
+    {
+        public Task EnableNavigationInterceptionAsync()
+        {
+            throw new InvalidOperationException("Navigation interception calls cannot be issued during server-side prerendering, because the page has not yet loaded in the browser. " +
+                "Prerendered components must wrap any navigation interception calls in conditional logic to ensure those interop calls are not attempted during prerendering.");
+        }
+    }
+}

src/Mvc/test/Mvc.FunctionalTests/ComponentRenderingFunctionalTests.cs

@@ -37,7 +37,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent("\n<p>Hello world!</p>", "Greetings", content);
@@ -53,7 +53,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent("\n<p>Hello world!</p>", "Greetings", content);
@@ -68,7 +68,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components/routable");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent("\nRouter component\n<p>Routed successfully</p>", "Routing", content);
@@ -84,7 +84,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components/routable");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent("\nRouter component\n<p>Routed successfully</p>", "Routing", content);
@@ -100,7 +100,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components/false");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent("<p>Hello world!</p>", "Greetings", content, unwrap: true);
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components/routable/false");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent("Router component\n<p>Routed successfully</p>", "Routing", content, unwrap: true);
@@ -194,7 +194,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             var response = await client.GetAsync("http://localhost/components");
 
             // Assert
-            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
             var content = await response.Content.ReadAsStringAsync();
 
             AssertComponent(expectedHtml, "FetchData", content);

src/Mvc/test/WebSites/BasicWebSite/RazorComponents/Fallback.razor

@@ -1 +0,0 @@
-<p>Route not found</p>

src/Mvc/test/WebSites/BasicWebSite/RazorComponents/RouterContainer.razor

@@ -1,6 +1,7 @@
 @using Microsoft.AspNetCore.Components.Routing
 Router component
-<Router 
+<Router AppAssembly="System.Reflection.Assembly.GetAssembly(typeof(RouterContainer))">
-        AppAssembly="System.Reflection.Assembly.GetAssembly(typeof(RouterContainer))"
+    <NotFoundContent>
-        FallbackComponent="typeof(Fallback)">
+        <p>Route not found</p>
+    </NotFoundContent>
 </Router>