Merge branch 'release/5.0-preview8'

AspNetCore.sln

@@ -1427,6 +1427,20 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.AspNetCore.Compon
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.AspNetCore.Components.Web.Extensions.Tests", "src\Components\Web.Extensions\test\Microsoft.AspNetCore.Components.Web.Extensions.Tests.csproj", "{157605CB-5170-4C1A-980F-4BAE42DB60DE}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "testassets", "testassets", "{2531F00A-54EB-4074-9C0B-9AF9FB3679DC}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "BasicTestApp", "src\Components\test\testassets\BasicTestApp\BasicTestApp.csproj", "{85D67E40-4B11-48ED-8C43-34590A1FB9ED}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "LazyTestContentPackage", "src\Components\test\testassets\LazyTestContentPackage\LazyTestContentPackage.csproj", "{C0EF53A5-5A94-4849-86B0-2297EA08D649}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ComponentsApp.App", "src\Components\test\testassets\ComponentsApp.App\ComponentsApp.App.csproj", "{4FDD820F-8397-41B7-956E-F257DD044BD8}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ComponentsApp.Server", "src\Components\test\testassets\ComponentsApp.Server\ComponentsApp.Server.csproj", "{CA7C7A53-446F-453A-A57B-78BB1443B8A8}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestContentPackage", "src\Components\test\testassets\TestContentPackage\TestContentPackage.csproj", "{B32C5882-2313-40D0-A003-2FF33724CFE6}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Components.TestServer", "src\Components\test\testassets\TestServer\Components.TestServer.csproj", "{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}"
+EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Sdk", "Sdk", "{FED4267E-E5E4-49C5-98DB-8B3F203596EE}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Microsoft.NET.Sdk.BlazorWebAssembly", "src\Components\WebAssembly\Sdk\src\Microsoft.NET.Sdk.BlazorWebAssembly.csproj", "{6B2734BF-C61D-4889-ABBF-456A4075D59B}"
@@ -6763,6 +6777,78 @@ Global
 		{157605CB-5170-4C1A-980F-4BAE42DB60DE}.Release|x64.Build.0 = Release|Any CPU
 		{157605CB-5170-4C1A-980F-4BAE42DB60DE}.Release|x86.ActiveCfg = Release|Any CPU
 		{157605CB-5170-4C1A-980F-4BAE42DB60DE}.Release|x86.Build.0 = Release|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Debug|x64.Build.0 = Debug|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Debug|x86.Build.0 = Debug|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Release|Any CPU.Build.0 = Release|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Release|x64.ActiveCfg = Release|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Release|x64.Build.0 = Release|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Release|x86.ActiveCfg = Release|Any CPU
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED}.Release|x86.Build.0 = Release|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Debug|x64.Build.0 = Debug|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Debug|x86.Build.0 = Debug|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Release|Any CPU.Build.0 = Release|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Release|x64.ActiveCfg = Release|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Release|x64.Build.0 = Release|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Release|x86.ActiveCfg = Release|Any CPU
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649}.Release|x86.Build.0 = Release|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Debug|x64.Build.0 = Debug|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Debug|x86.Build.0 = Debug|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Release|x64.ActiveCfg = Release|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Release|x64.Build.0 = Release|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Release|x86.ActiveCfg = Release|Any CPU
+		{4FDD820F-8397-41B7-956E-F257DD044BD8}.Release|x86.Build.0 = Release|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Debug|x64.Build.0 = Debug|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Debug|x86.Build.0 = Debug|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Release|x64.ActiveCfg = Release|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Release|x64.Build.0 = Release|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Release|x86.ActiveCfg = Release|Any CPU
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8}.Release|x86.Build.0 = Release|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Debug|x64.Build.0 = Debug|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Debug|x86.Build.0 = Debug|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Release|Any CPU.Build.0 = Release|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Release|x64.ActiveCfg = Release|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Release|x64.Build.0 = Release|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Release|x86.ActiveCfg = Release|Any CPU
+		{B32C5882-2313-40D0-A003-2FF33724CFE6}.Release|x86.Build.0 = Release|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Debug|x64.Build.0 = Debug|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Debug|x86.Build.0 = Debug|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Release|Any CPU.Build.0 = Release|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Release|x64.ActiveCfg = Release|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Release|x64.Build.0 = Release|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Release|x86.ActiveCfg = Release|Any CPU
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00}.Release|x86.Build.0 = Release|Any CPU
 		{6B2734BF-C61D-4889-ABBF-456A4075D59B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{6B2734BF-C61D-4889-ABBF-456A4075D59B}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{6B2734BF-C61D-4889-ABBF-456A4075D59B}.Debug|x64.ActiveCfg = Debug|Any CPU
@@ -7634,6 +7720,13 @@ Global
 		{F71FE795-9923-461B-9809-BB1821A276D0} = {60D51C98-2CC0-40DF-B338-44154EFEE2FF}
 		{8294A74F-7DAA-4B69-BC56-7634D93C9693} = {F71FE795-9923-461B-9809-BB1821A276D0}
 		{157605CB-5170-4C1A-980F-4BAE42DB60DE} = {F71FE795-9923-461B-9809-BB1821A276D0}
+		{2531F00A-54EB-4074-9C0B-9AF9FB3679DC} = {0508E463-0269-40C9-B5C2-3B600FB2A28B}
+		{85D67E40-4B11-48ED-8C43-34590A1FB9ED} = {2531F00A-54EB-4074-9C0B-9AF9FB3679DC}
+		{C0EF53A5-5A94-4849-86B0-2297EA08D649} = {2531F00A-54EB-4074-9C0B-9AF9FB3679DC}
+		{4FDD820F-8397-41B7-956E-F257DD044BD8} = {2531F00A-54EB-4074-9C0B-9AF9FB3679DC}
+		{CA7C7A53-446F-453A-A57B-78BB1443B8A8} = {2531F00A-54EB-4074-9C0B-9AF9FB3679DC}
+		{B32C5882-2313-40D0-A003-2FF33724CFE6} = {2531F00A-54EB-4074-9C0B-9AF9FB3679DC}
+		{26F88A06-319C-43F3-9FD9-8BC2D29F8C00} = {2531F00A-54EB-4074-9C0B-9AF9FB3679DC}
 		{FED4267E-E5E4-49C5-98DB-8B3F203596EE} = {562D5067-8CD8-4F19-BCBB-873204932C61}
 		{6B2734BF-C61D-4889-ABBF-456A4075D59B} = {FED4267E-E5E4-49C5-98DB-8B3F203596EE}
 		{83371889-9A3E-4D16-AE77-EB4F83BC6374} = {FED4267E-E5E4-49C5-98DB-8B3F203596EE}

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

@@ -68,12 +68,12 @@ namespace Microsoft.AspNetCore.Components.Routing
         /// <summary>
         /// Get or sets the content to display when asynchronous navigation is in progress.
         /// </summary>
-        [Parameter] public RenderFragment Navigating { get; set; }
+        [Parameter] public RenderFragment? Navigating { get; set; }
 
         /// <summary>
         /// Gets or sets a handler that should be called before navigating to a new page.
         /// </summary>
-        [Parameter] public Func<NavigationContext, Task> OnNavigateAsync { get; set; }
+        [Parameter] public Func<NavigationContext, Task>? OnNavigateAsync { get; set; }
 
         private RouteTable Routes { get; set; }
 
@@ -195,10 +195,6 @@ namespace Microsoft.AspNetCore.Components.Routing
 
         private async ValueTask<bool> RunOnNavigateAsync(string path, Task previousOnNavigate)
         {
-            if (OnNavigateAsync == null)
-            {
-                return true;
-            }
 
             // Cancel the CTS instead of disposing it, since disposing does not
             // actually cancel and can cause unintended Object Disposed Exceptions.
@@ -210,6 +206,11 @@ namespace Microsoft.AspNetCore.Components.Routing
             // invocation.
             await previousOnNavigate;
 
+            if (OnNavigateAsync == null)
+            {
+                return true;
+            }
+
             _onNavigateCts = new CancellationTokenSource();
             var navigateContext = new NavigationContext(path, _onNavigateCts.Token);
 
@@ -227,14 +228,12 @@ namespace Microsoft.AspNetCore.Components.Routing
                 if (e.CancellationToken != navigateContext.CancellationToken)
                 {
                     var rethrownException = new InvalidOperationException("OnNavigateAsync can only be cancelled via NavigateContext.CancellationToken.", e);
-                    _renderHandle.Render(builder => ExceptionDispatchInfo.Capture(rethrownException).Throw());
+                    _renderHandle.Render(builder => ExceptionDispatchInfo.Throw(rethrownException));
-                    return false;
                 }
             }
             catch (Exception e)
             {
-                _renderHandle.Render(builder => ExceptionDispatchInfo.Capture(e).Throw());
+                _renderHandle.Render(builder => ExceptionDispatchInfo.Throw(e));
-                return false;
             }
 
             return false;

src/Components/Web.Extensions/src/HeadManagement/HeadManagementJSRuntimeExtensions.cs

@@ -0,0 +1,28 @@
+// 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.JSInterop;
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    internal static class HeadManagementJSRuntimeExtensions
+    {
+        private const string JsFunctionsPrefix = "_blazorHeadManager";
+
+        public static ValueTask SetTitleAsync(this IJSRuntime jsRuntime, string title)
+        {
+            return jsRuntime.InvokeVoidAsync($"{JsFunctionsPrefix}.setTitle", title);
+        }
+
+        public static ValueTask AddOrUpdateHeadTagAsync(this IJSRuntime jsRuntime, TagElement tag, string id)
+        {
+            return jsRuntime.InvokeVoidAsync($"{JsFunctionsPrefix}.addOrUpdateHeadTag", tag, id);
+        }
+
+        public static ValueTask RemoveHeadTagAsync(this IJSRuntime jsRuntime, string id)
+        {
+            return jsRuntime.InvokeVoidAsync($"{JsFunctionsPrefix}.removeHeadTag", id);
+        }
+    }
+}

src/Components/Web.Extensions/src/HeadManagement/HeadTagBase.cs

@@ -0,0 +1,67 @@
+// 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.Collections.Generic;
+using System.Text.Json;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Rendering;
+using Microsoft.JSInterop;
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    /// <summary>
+    /// Serves as a base for components that represent tags in the HTML head.
+    /// </summary>
+    public abstract class HeadTagBase : ComponentBase, IDisposable
+    {
+        private readonly string _id = Guid.NewGuid().ToString("N");
+
+        private TagElement _tagElement;
+
+        private bool _hasRendered;
+
+        [Inject]
+        private IJSRuntime JSRuntime { get; set; } = default!;
+
+        /// <summary>
+        /// Gets or sets a collection of additional attributes that will be applied to the meta element.
+        /// </summary>
+        [Parameter(CaptureUnmatchedValues = true)]
+        public IReadOnlyDictionary<string, object>? Attributes { get; set; }
+
+        /// <summary>
+        /// Gets the name of the tag being represented.
+        /// </summary>
+        protected abstract string TagName { get; }
+
+        /// <inheritdoc />
+        protected override void OnParametersSet()
+        {
+            _tagElement = new TagElement(TagName, Attributes);
+        }
+
+        /// <inheritdoc />
+        protected override async Task OnAfterRenderAsync(bool firstRender)
+        {
+            _hasRendered = true;
+
+            await JSRuntime.AddOrUpdateHeadTagAsync(_tagElement, _id);
+        }
+
+        /// <inheritdoc />
+        protected override void BuildRenderTree(RenderTreeBuilder builder)
+        {
+            builder.AddMarkupContent(0, $"<!--Head:{JsonSerializer.Serialize(_tagElement, JsonSerializerOptionsProvider.Options)}-->");
+        }
+
+        /// <inheritdoc />
+        public void Dispose()
+        {
+            if (_hasRendered)
+            {
+                _ = JSRuntime.RemoveHeadTagAsync(_id);
+            }
+        }
+    }
+}

src/Components/Web.Extensions/src/HeadManagement/Link.cs

@@ -0,0 +1,14 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    /// <summary>
+    /// A component that adds a link tag to the HTML head.
+    /// </summary>
+    public sealed class Link : HeadTagBase
+    {
+        /// <inheritdoc />
+        protected override string TagName => "link";
+    }
+}

src/Components/Web.Extensions/src/HeadManagement/Meta.cs

@@ -0,0 +1,14 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    /// <summary>
+    /// A component that adds a meta tag to the HTML head.
+    /// </summary>
+    public sealed class Meta : HeadTagBase
+    {
+        /// <inheritdoc />
+        protected override string TagName => "meta";
+    }
+}

src/Components/Web.Extensions/src/HeadManagement/TagElement.cs

@@ -0,0 +1,22 @@
+// 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.Collections.Generic;
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    internal readonly struct TagElement
+    {
+        public string Type => "tag";
+
+        public string TagName { get; }
+
+        public IReadOnlyDictionary<string, object>? Attributes { get; }
+
+        public TagElement(string tagName, IReadOnlyDictionary<string, object>? attributes)
+        {
+            TagName = tagName;
+            Attributes = attributes;
+        }
+    }
+}

src/Components/Web.Extensions/src/HeadManagement/Title.cs

@@ -0,0 +1,37 @@
+// 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.Text.Json;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Rendering;
+using Microsoft.JSInterop;
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    /// <summary>
+    /// A component that changes the title of the document.
+    /// </summary>
+    public sealed class Title : ComponentBase
+    {
+        [Inject]
+        private IJSRuntime JSRuntime { get; set; } = default!;
+
+        /// <summary>
+        /// Gets or sets the value to use as the document's title.
+        /// </summary>
+        [Parameter]
+        public string Value { get; set; } = string.Empty;
+
+        /// <inheritdoc />
+        protected override async Task OnAfterRenderAsync(bool firstRender)
+        {
+            await JSRuntime.SetTitleAsync(Value);
+        }
+
+        /// <inheritdoc />
+        protected override void BuildRenderTree(RenderTreeBuilder builder)
+        {
+            builder.AddMarkupContent(0, $"<!--Head:{JsonSerializer.Serialize(new TitleElement(Value), JsonSerializerOptionsProvider.Options)}-->");
+        }
+    }
+}

src/Components/Web.Extensions/src/HeadManagement/TitleElement.cs

@@ -0,0 +1,17 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Components.Web.Extensions.Head
+{
+    internal readonly struct TitleElement
+    {
+        public string Type => "title";
+
+        public string Title { get; }
+
+        public TitleElement(string title)
+        {
+            Title = title;
+        }
+    }
+}

src/Components/Web.Extensions/src/Microsoft.AspNetCore.Components.Web.Extensions.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk.Razor">
 
   <PropertyGroup>
     <TargetFramework>$(DefaultNetCoreTargetFramework)</TargetFramework>
@@ -9,6 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Reference Include="Microsoft.AspNetCore.Components" />
     <Reference Include="Microsoft.AspNetCore.DataProtection" />
     <Reference Include="Microsoft.JSInterop" />
   </ItemGroup>

src/Components/Web.Extensions/src/Properties/AssemblyInfo.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("Microsoft.AspNetCore.Components.Web.Extensions.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]

src/Components/Web.Extensions/src/wwwroot/headManager.js

@@ -0,0 +1,102 @@
+(function () {
+    // Local helpers
+
+    const blazorIdAttributeName = '_blazor_id';
+    const headCommentRegularExpression = /\W*Head:[^{]*(.*)$/;
+    const prerenderedTags = [];
+
+    function createHeadTag({ tagName, attributes }, id) {
+        const tagElement = document.createElement(tagName);
+
+        // The id is undefined during prerendering
+        if (id) {
+            tagElement.setAttribute(blazorIdAttributeName, id);
+        }
+
+        if (attributes) {
+            Object.keys(attributes).forEach(key => {
+                tagElement.setAttribute(key, attributes[key]);
+            });
+        }
+
+        document.head.appendChild(tagElement);
+
+        return tagElement;
+    }
+
+    function resolvePrerenderedHeadComponents(node) {
+        node.childNodes.forEach((childNode) => {
+            const headElement = parseHeadComment(childNode);
+
+            if (headElement) {
+                applyPrerenderedHeadComponent(headElement);
+            } else {
+                resolvePrerenderedHeadComponents(childNode);
+            }
+        });
+    }
+
+    function applyPrerenderedHeadComponent(headElement) {
+        switch (headElement.type) {
+            case 'title':
+                setTitle(headElement.title);
+                break;
+            case 'tag':
+                const tag = createHeadTag(headElement);
+                prerenderedTags.push(tag);
+                break;
+            default:
+                throw new Error(`Invalid head element type '${headElement.type}'.`);
+        }
+    }
+
+    function parseHeadComment(node) {
+        if (!node || node.nodeType != Node.COMMENT_NODE) {
+            return;
+        }
+
+        const commentText = node.textContent;
+
+        if (!commentText) {
+            return;
+        }
+
+        const definition = headCommentRegularExpression.exec(commentText);
+        const json = definition && definition[1];
+
+        return json && JSON.parse(json);
+    }
+
+    function removePrerenderedHeadTags() {
+        prerenderedTags.forEach((tag) => {
+            tag.remove();
+        });
+
+        prerenderedTags.length = 0;
+    }
+
+    // Exported functions
+
+    function setTitle(title) {
+        document.title = title;
+    }
+
+    function addOrUpdateHeadTag(tag, id) {
+        removePrerenderedHeadTags();
+        removeHeadTag(id);
+        createHeadTag(tag, id);
+    }
+
+    function removeHeadTag(id) {
+        let tag = document.head.querySelector(`[${blazorIdAttributeName}='${id}']`);
+        tag && tag.remove();
+    }
+
+    window._blazorHeadManager = {
+        setTitle,
+        addOrUpdateHeadTag,
+        removeHeadTag,
+    };
+
+    resolvePrerenderedHeadComponents(document);
+})();

src/Components/Web.JS/src/Platform/Mono/MonoPlatform.ts

@@ -324,9 +324,18 @@ function createEmscriptenModuleInstance(resourceLoader: WebAssemblyResourceLoade
       const assembliesToLoad = BINDING.mono_array_to_js_array<System_String, string>(assembliesToLoadDotNetArray);
       const lazyAssemblies = resourceLoader.bootConfig.resources.lazyAssembly;
 
-      if (lazyAssemblies) {
+      if (!lazyAssemblies) {
-        const resourcePromises = Promise.all(assembliesToLoad
+        throw new Error("No assemblies have been marked as lazy-loadable. Use the 'BlazorWebAssemblyLazyLoad' item group in your project file to enable lazy loading an assembly.");
-            .filter(assembly => lazyAssemblies.hasOwnProperty(assembly))
+      }
+
+      var assembliesMarkedAsLazy = assembliesToLoad.filter(assembly => lazyAssemblies.hasOwnProperty(assembly));
+
+      if (assembliesMarkedAsLazy.length != assembliesToLoad.length) {
+        var notMarked = assembliesToLoad.filter(assembly => !assembliesMarkedAsLazy.includes(assembly));
+        throw new Error(`${notMarked.join()} must be marked with 'BlazorWebAssemblyLazyLoad' item group in your project file to allow lazy-loading.`);
+      }
+
+      const resourcePromises = Promise.all(assembliesMarkedAsLazy
             .map(assembly => resourceLoader.loadResource(assembly, `_framework/${assembly}`, lazyAssemblies[assembly], 'assembly'))
             .map(async resource => (await resource.response).arrayBuffer()));
 
@@ -345,8 +354,6 @@ function createEmscriptenModuleInstance(resourceLoader: WebAssemblyResourceLoade
           return resourcesToLoad.length;
         }));
       }
-      return BINDING.js_to_mono_obj(Promise.resolve(0));
-    }
   });
 
   module.postRun.push(() => {

src/Components/Web.JS/src/Rendering/LogicalElements.ts

@@ -132,8 +132,10 @@ export function removeLogicalChild(parent: LogicalElement, childIndex: number) {
   // If it's a logical container, also remove its descendants
   if (childToRemove instanceof Comment) {
     const grandchildrenArray = getLogicalChildrenArray(childToRemove);
-    while (grandchildrenArray.length > 0) {
+    if (grandchildrenArray) {
-      removeLogicalChild(childToRemove, 0);
+      while (grandchildrenArray.length > 0) {
+        removeLogicalChild(childToRemove, 0);
+      }
     }
   }
 

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs

@@ -130,7 +130,7 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting
         /// <summary>
         /// Gets the logging builder for configuring logging services.
         /// </summary>
-        public ILoggingBuilder Logging { get;  }
+        public ILoggingBuilder Logging { get; }
 
         /// <summary>
         /// Registers a <see cref="IServiceProviderFactory{TBuilder}" /> instance to be used to create the <see cref="IServiceProvider" />.
@@ -189,7 +189,7 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting
             Services.AddSingleton<IJSRuntime>(DefaultWebAssemblyJSRuntime.Instance);
             Services.AddSingleton<NavigationManager>(WebAssemblyNavigationManager.Instance);
             Services.AddSingleton<INavigationInterception>(WebAssemblyNavigationInterception.Instance);
-            Services.AddSingleton(provider => new LazyAssemblyLoader(provider));
+            Services.AddSingleton(new LazyAssemblyLoader(DefaultWebAssemblyJSRuntime.Instance));
             Services.AddLogging(builder => {
                 builder.AddProvider(new WebAssemblyConsoleLoggerProvider(DefaultWebAssemblyJSRuntime.Instance));
             });

src/Components/WebAssembly/WebAssembly/src/Services/LazyAssemblyLoader.cs

@@ -9,7 +9,6 @@ using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Runtime.Loader;
 using System.Threading.Tasks;
-using Microsoft.Extensions.DependencyInjection;
 using Microsoft.JSInterop;
 using Microsoft.JSInterop.WebAssembly;
 
@@ -20,19 +19,18 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Services
     ///
     /// Supports finding pre-loaded assemblies in a server or pre-rendering context.
     /// </summary>
-    public class LazyAssemblyLoader
+    public sealed class LazyAssemblyLoader
     {
         internal const string GetDynamicAssemblies = "window.Blazor._internal.getLazyAssemblies";
         internal const string ReadDynamicAssemblies = "window.Blazor._internal.readLazyAssemblies";
 
-        private List<Assembly> _loadedAssemblyCache = new List<Assembly>();
+        private readonly IJSRuntime _jsRuntime;
+        private readonly HashSet<string> _loadedAssemblyCache;
 
-        private readonly IServiceProvider _provider;
+        public LazyAssemblyLoader(IJSRuntime jsRuntime)
-
-        public LazyAssemblyLoader(IServiceProvider provider)
         {
-            _provider = provider;
+            _jsRuntime = jsRuntime;
-            _loadedAssemblyCache = AppDomain.CurrentDomain.GetAssemblies().ToList();
+            _loadedAssemblyCache = AppDomain.CurrentDomain.GetAssemblies().Select(a => a.GetName().Name + ".dll").ToHashSet();
         }
 
         /// <summary>
@@ -55,37 +53,45 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Services
 
         private Task<IEnumerable<Assembly>> LoadAssembliesInServerAsync(IEnumerable<string> assembliesToLoad)
         {
-            var loadedAssemblies = _loadedAssemblyCache.Where(assembly =>
+            var loadedAssemblies = new List<Assembly>();
-                assembliesToLoad.Contains(assembly.GetName().Name + ".dll"));
 
-            if (loadedAssemblies.Count() != assembliesToLoad.Count())
+            try
             {
-                var unloadedAssemblies = assembliesToLoad.Except(loadedAssemblies.Select(a => a.GetName().Name + ".dll"));
+                foreach (var assemblyName in assembliesToLoad)
-                throw new InvalidOperationException($"Unable to find the following assemblies: {string.Join(",", unloadedAssemblies)}. Make sure that the appplication is referencing the assemblies and that they are present in the output folder.");
+                {
+                    loadedAssemblies.Add(Assembly.Load(Path.GetFileNameWithoutExtension(assemblyName)));
+                }
+            }
+            catch (FileNotFoundException ex)
+            {
+                throw new InvalidOperationException($"Unable to find the following assembly: {ex.FileName}. Make sure that the appplication is referencing the assemblies and that they are present in the output folder.");
             }
 
-            return Task.FromResult(loadedAssemblies);
+            return Task.FromResult<IEnumerable<Assembly>>(loadedAssemblies);
         }
 
         private async Task<IEnumerable<Assembly>> LoadAssembliesInClientAsync(IEnumerable<string> assembliesToLoad)
         {
-            var jsRuntime = _provider.GetRequiredService<IJSRuntime>();
+            // Check to see if the assembly has already been loaded and avoids reloading it if so.
-            // Only load assemblies that haven't already been lazily-loaded
+            // Note: in the future, as an extra precuation, we can call `Assembly.Load` and check
-            var newAssembliesToLoad = assembliesToLoad.Except(_loadedAssemblyCache.Select(a => a.GetName().Name + ".dll"));
+            // to see if it throws FileNotFound to ensure that an assembly hasn't been loaded
+            // between when the cache of loaded assemblies was instantiated in the constructor
+            // and the invocation of this method.
+            var newAssembliesToLoad = assembliesToLoad.Where(assembly => !_loadedAssemblyCache.Contains(assembly));
             var loadedAssemblies = new List<Assembly>();
 
-            var count = (int)await ((WebAssemblyJSRuntime)jsRuntime).InvokeUnmarshalled<string[], object, object, Task<object>>(
+            var count = (int)await ((WebAssemblyJSRuntime)_jsRuntime).InvokeUnmarshalled<string[], object, object, Task<object>>(
-                GetDynamicAssemblies,
+               GetDynamicAssemblies,
-                assembliesToLoad.ToArray(),
+               newAssembliesToLoad.ToArray(),
-                null,
+               null,
-                null);
+               null);
 
             if (count == 0)
             {
                 return loadedAssemblies;
             }
 
-            var assemblies = ((WebAssemblyJSRuntime)jsRuntime).InvokeUnmarshalled<object, object, object, object[]>(
+            var assemblies = ((WebAssemblyJSRuntime)_jsRuntime).InvokeUnmarshalled<object, object, object, object[]>(
                 ReadDynamicAssemblies,
                 null,
                 null,
@@ -99,7 +105,7 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Services
                 // into the default app context.
                 var loadedAssembly = AssemblyLoadContext.Default.LoadFromStream(new MemoryStream(assembly));
                 loadedAssemblies.Add(loadedAssembly);
-                _loadedAssemblyCache.Add(loadedAssembly);
+                _loadedAssemblyCache.Add(loadedAssembly.GetName().Name + ".dll");
             }
 
             return loadedAssemblies;

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

@@ -81,6 +81,51 @@ namespace Microsoft.AspNetCore.Components.E2ETest.ServerExecutionTests
             AssertLogDoesNotContainCriticalMessages("Could not load file or assembly 'Newtonsoft.Json");
         }
 
+        [Fact]
+        public void CanInfluenceHeadDuringPrerender()
+        {
+            Navigate("/prerendered/prerendered-head");
+
+            var metaWithBindings = Browser.FindElement(By.Id("meta-with-bindings"));
+            var metaNoBindings = Browser.FindElement(By.Id("meta-no-bindings"));
+
+            // Validate updated head during prerender
+            Browser.Equal("Initial title", () => Browser.Title);
+            Browser.Equal("Initial meta content", () => metaWithBindings.GetAttribute("content"));
+            Browser.Equal("Immutable meta content", () => metaNoBindings.GetAttribute("content"));
+
+            BeginInteractivity();
+
+            // Wait for elements to be recreated with internal ids to permit mutation
+            metaWithBindings = WaitForNewElement(metaWithBindings, "meta-with-bindings");
+            metaNoBindings = WaitForNewElement(metaNoBindings, "meta-no-bindings");
+
+            // Validate updated head after prerender
+            Browser.Equal("Initial title", () => Browser.Title);
+            Browser.Equal("Initial meta content", () => metaWithBindings.GetAttribute("content"));
+            Browser.Equal("Immutable meta content", () => metaNoBindings.GetAttribute("content"));
+
+            // Change parameter of meta component
+            var inputMetaBinding = Browser.FindElement(By.Id("input-meta-binding"));
+            inputMetaBinding.Clear();
+            inputMetaBinding.SendKeys("Updated meta content\n");
+
+            // Wait for meta tag to be recreated with new attributes
+            metaWithBindings = WaitForNewElement(metaWithBindings, "meta-with-bindings");
+
+            // Validate new meta content attribute
+            Browser.Equal("Updated meta content", () => metaWithBindings.GetAttribute("content"));
+
+            IWebElement WaitForNewElement(IWebElement existingElement, string id)
+            {
+                var newElement = existingElement;
+
+                Browser.NotEqual(existingElement, () => newElement = Browser.FindElement(By.Id(id)) ?? newElement);
+
+                return newElement;
+            }
+        }
+
         [Fact]
         public void CanReadUrlHashOnlyOnceConnected()
         {

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

@@ -0,0 +1,176 @@
+// 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.Linq;
+using BasicTestApp;
+using Microsoft.AspNetCore.Components.E2ETest;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
+using Microsoft.AspNetCore.E2ETesting;
+using OpenQA.Selenium;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Components.E2ETests.Tests
+{
+    public class HeadComponentsTest : ServerTestBase<ToggleExecutionModeServerFixture<Program>>
+    {
+        public HeadComponentsTest(
+            BrowserFixture browserFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
+            ITestOutputHelper output)
+            : base(browserFixture, serverFixture, output)
+        {
+        }
+
+        protected override void InitializeAsyncCore()
+        {
+            Navigate(ServerPathBase, noReload: _serverFixture.ExecutionMode == ExecutionMode.Client);
+            Browser.MountTestComponent<ModifyHeadComponent>();
+        }
+
+        [Fact]
+        public void Title_DoesChangeDocumentTitle()
+        {
+            var titleCount = 3;
+            var titleButtonsById = Enumerable.Range(0, titleCount)
+                .Select(i => (i, Browser.FindElement(By.Id($"button-title-{i}"))))
+                .ToList();
+
+            Assert.All(titleButtonsById, buttonById =>
+            {
+                var (id, button) = buttonById;
+                button.Click();
+
+                Browser.Equal($"Title {id}", () => Browser.Title);
+            });
+        }
+
+        [Fact]
+        public void Title_DeepestComponentHasPriority()
+        {
+            var nestedTitleButton = Browser.FindElement(By.Id("button-title-nested"));
+            nestedTitleButton.Click();
+
+            Browser.Equal("Layer 4", () => Browser.Title);
+        }
+
+        [Fact]
+        public void Meta_AddsAndRemovesElements()
+        {
+            var metaCount = 3;
+            var metaButtonsById = Enumerable.Range(0, metaCount)
+                .Select(i => (i, Browser.FindElement(By.Id($"button-meta-{i}"))))
+                .ToList();
+
+            // Validate adding elements
+            Assert.All(metaButtonsById, buttonById =>
+            {
+                var (id, button) = buttonById;
+                button.Click();
+
+                Browser.Exists(By.Id($"Meta {id}"));
+            });
+
+            // Validate removing elements
+            Assert.All(metaButtonsById, buttonById =>
+            {
+                var (id, button) = buttonById;
+                button.Click();
+
+                Browser.DoesNotExist(By.Id($"Meta {id}"));
+            });
+        }
+
+        [Fact]
+        public void Meta_UpdatesSameElementWhenComponentPropertyChanged()
+        {
+            var metaAttributeInput1 = Browser.FindElement(By.Id("meta-attr-input-1"));
+            var metaAttributeInput2 = Browser.FindElement(By.Id("meta-attr-input-2"));
+            var metaElement = FindMetaElement();
+
+            // Validate initial attribute values
+            Browser.Equal("First attribute", () => metaElement.GetAttribute("attr1"));
+            Browser.Equal("Second attribute", () => metaElement.GetAttribute("attr2"));
+
+            // Update the first parameter of the component
+            metaAttributeInput1.Clear();
+            metaAttributeInput1.SendKeys("hello\n");
+            metaElement = FindMetaElement();
+
+            // Validate first attribute updated
+            Browser.Equal("hello", () => metaElement.GetAttribute("attr1"));
+            Browser.Equal("Second attribute", () => metaElement.GetAttribute("attr2"));
+
+            // Update the second parameter of the component
+            metaAttributeInput2.Clear();
+            metaAttributeInput2.SendKeys("world\n");
+            metaElement = FindMetaElement();
+
+            // Validate second attribute updated
+            Browser.Equal("hello", () => metaElement.GetAttribute("attr1"));
+            Browser.Equal("world", () => metaElement.GetAttribute("attr2"));
+
+            IWebElement FindMetaElement() => Browser.FindElements(By.Id("meta-with-bindings")).Single();
+        }
+
+        [Fact]
+        public void Link_AddsAndRemovesElements()
+        {
+            var linkCount = 3;
+            var linkButtonsById = Enumerable.Range(0, linkCount)
+                .Select(i => (i, Browser.FindElement(By.Id($"button-link-{i}"))))
+                .ToList();
+
+            // Validate adding elements
+            Assert.All(linkButtonsById, buttonById =>
+            {
+                var (id, button) = buttonById;
+                button.Click();
+
+                Browser.Exists(By.Id($"Link {id}"));
+            });
+
+            // Validate removing elements
+            Assert.All(linkButtonsById, buttonById =>
+            {
+                var (id, button) = buttonById;
+                button.Click();
+
+                Browser.DoesNotExist(By.Id($"Link {id}"));
+            });
+        }
+
+        [Fact]
+        public void Link_UpdatesSameElementWhenComponentPropertyChanged()
+        {
+            var linkAttributeInput1 = Browser.FindElement(By.Id("link-attr-input-1"));
+            var linkAttributeInput2 = Browser.FindElement(By.Id("link-attr-input-2"));
+            var linkElement = FindLinkElement();
+
+            // Validate initial attribute values
+            Browser.Equal("First attribute", () => linkElement.GetAttribute("attr1"));
+            Browser.Equal("Second attribute", () => linkElement.GetAttribute("attr2"));
+
+            // Update the first parameter of the component
+            linkAttributeInput1.Clear();
+            linkAttributeInput1.SendKeys("hello\n");
+            linkElement = FindLinkElement();
+
+            // Validate first attribute updated
+            Browser.Equal("hello", () => linkElement.GetAttribute("attr1"));
+            Browser.Equal("Second attribute", () => linkElement.GetAttribute("attr2"));
+
+            // Update the second parameter of the component
+            linkAttributeInput2.Clear();
+            linkAttributeInput2.SendKeys("world\n");
+            linkElement = FindLinkElement();
+
+            // Validate second attribute updated
+            Browser.Equal("hello", () => linkElement.GetAttribute("attr1"));
+            Browser.Equal("world", () => linkElement.GetAttribute("attr2"));
+
+            IWebElement FindLinkElement() => Browser.FindElements(By.Id("link-with-bindings")).Single();
+        }
+    }
+}

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

@@ -111,6 +111,21 @@ namespace Microsoft.AspNetCore.Components.E2ETest.Tests
             Assert.True(renderedElement.Displayed);
         }
 
+        [Fact]
+        public void ThrowsErrorForUnavailableAssemblies()
+        {
+            // Navigate to a page with lazy loaded assemblies for the first time
+            SetUrlViaPushState("/Other");
+            var app = Browser.MountTestComponent<TestRouterWithLazyAssembly>();
+
+            // Should've thrown an error for unhandled error
+            var errorUiElem = Browser.Exists(By.Id("blazor-error-ui"), TimeSpan.FromSeconds(10));
+            Assert.NotNull(errorUiElem);
+
+
+            AssertLogContainsCriticalMessages("DoesNotExist.dll must be marked with 'BlazorWebAssemblyLazyLoad' item group in your project file to allow lazy-loading.");
+        }
+
         private string SetUrlViaPushState(string relativeUri)
         {
             var pathBaseWithoutHash = ServerPathBase.Split('#')[0];
@@ -145,5 +160,18 @@ namespace Microsoft.AspNetCore.Components.E2ETest.Tests
                 });
             }
         }
+
+        void AssertLogContainsCriticalMessages(params string[] messages)
+        {
+            var log = Browser.Manage().Logs.GetLog(LogType.Browser);
+            foreach (var message in messages)
+            {
+                Assert.Contains(log, entry =>
+                {
+                    return entry.Level == LogLevel.Severe
+                    && entry.Message.Contains(message);
+                });
+            }
+        }
     }
 }

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

@@ -57,6 +57,7 @@
         <option value="BasicTestApp.LoggingComponent">Logging</option>
         <option value="BasicTestApp.LongRunningInterop">Long running interop</option>
         <option value="BasicTestApp.MarkupBlockComponent">Markup blocks</option>
+        <option value="BasicTestApp.ModifyHeadComponent">Modify head</option>
         <option value="BasicTestApp.MouseEventComponent">Mouse events</option>
         <option value="BasicTestApp.MovingCheckboxesComponent">Moving checkboxes diff case</option>
         <option value="BasicTestApp.MultipleChildContent">Multiple child content</option>

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

@@ -0,0 +1,119 @@
+@using Microsoft.AspNetCore.Components.Web.Extensions.Head
+
+<p>
+    Multiple title elements:<br />
+
+    @for (int i = 0; i < 3; i++)
+    {
+        var titleId = i;
+
+        <button id="button-title-@i" @onclick="() => SetSelectedTitle(titleId)">
+            Title @titleId
+        </button>
+
+        if (selectedTitle == titleId)
+        {
+            <Title Value="@($"Title {titleId}")" />
+        }
+    }
+</p>
+
+<p>
+    Multiple meta elements:<br />
+
+    @for (int i = 0; i < metas.Length; i++)
+    {
+        var metaId = i;
+
+        <button id="button-meta-@i" @onclick="() => Toggle(metas, metaId)">
+            @GetToggleString(metas[metaId]) meta @metaId</button>
+
+        if (metas[metaId])
+        {
+            <Meta id="@($"Meta {metaId}")" />
+        }
+    }
+</p>
+
+<p>
+    Multiple link elements:<br />
+
+    @for (int i = 0; i < links.Length; i++)
+    {
+        var linkId = i;
+
+        <button id="button-link-@i" @onclick="() => Toggle(links, linkId)">
+            @GetToggleString(links[linkId]) link @linkId</button>
+
+        if (links[linkId])
+        {
+            <Link id="@($"Link {linkId}")" />
+        }
+    }
+</p>
+
+<p>
+    Nested title elements:<br />
+
+    <button id="button-title-nested" @onclick="() => SetSelectedTitle(3)">
+        Nested titles
+    </button>
+
+    @if (selectedTitle == 3)
+    {
+        <div>
+            <Title Value="Layer 1" />
+            <div>
+                <Title Value="Layer 2" />
+                <div>
+                    <Title Value="Layer 3" />
+                    <div>
+                        <Title Value="Layer 4" />
+                    </div>
+                </div>
+            </div>
+        </div>
+    }
+</p>
+
+<p>
+    Meta elements w/ bindings:<br />
+    <input id="meta-attr-input-1" @bind="@metaAttribute1" placeholder="Attribute 1" /><br />
+    <input id="meta-attr-input-2" @bind="@metaAttribute2" placeholder="Attribute 2" /><br />
+    <Meta id="meta-with-bindings" attr1="@metaAttribute1" attr2="@metaAttribute2" />
+</p>
+
+<p>
+    Link elements w/ bindings:<br />
+    <input id="link-attr-input-1" @bind="@linkAttribute1" placeholder="Attribute 1" /><br />
+    <input id="link-attr-input-2" @bind="@linkAttribute2" placeholder="Attribute 2" /><br />
+    <Link id="link-with-bindings" attr1="@linkAttribute1" attr2="@linkAttribute2" />
+</p>
+
+@code {
+    private readonly bool[] metas = Enumerable.Repeat(false, 3).ToArray();
+    private readonly bool[] links = Enumerable.Repeat(false, 3).ToArray();
+
+    private int selectedTitle = -1;
+
+    private string metaAttribute1 = "First attribute";
+    private string metaAttribute2 = "Second attribute";
+
+    private string linkAttribute1 = "First attribute";
+    private string linkAttribute2 = "Second attribute";
+
+    private void Toggle(bool[] states, int index)
+    {
+        states[index] = !states[index];
+        StateHasChanged();
+    }
+
+    private void SetSelectedTitle(int title)
+    {
+        selectedTitle = title;
+        StateHasChanged();
+    }
+
+    private string GetToggleString(bool b)
+        => b ? "Disable" : "Enable";
+}

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

@@ -0,0 +1,29 @@
+@page "/prerendered-head"
+
+@using Microsoft.AspNetCore.Components.Web.Extensions.Head
+@using Microsoft.JSInterop
+@inject IJSRuntime JSRuntime
+
+<p>
+    This component demonstrates that head components (i.e. Title, Meta, etc.) can take effect during prerendering
+    and become updatable when the circuit connects.
+</p>
+
+<p>
+    Title:<br />
+    <input id="title-input" @bind="title" placeholder="Set the title" />
+    <Title Value=@title />
+</p>
+
+<p>
+    Meta:<br />
+    <input id="input-meta-binding" @bind="metaContent" placeholder="Set the meta content" />
+    <Meta id="meta-with-bindings" content="@metaContent" />
+</p>
+
+<Meta id="meta-no-bindings" content="Immutable meta content" />
+
+@code {
+    private string title = "Initial title";
+    private string metaContent = "Initial meta content";
+}

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

@@ -1,6 +1,6 @@
 @using Microsoft.AspNetCore.Components.Routing
 @using System.Reflection
-@using Microsoft.AspNetCore.Components.WebAssembly.Services 
+@using Microsoft.AspNetCore.Components.WebAssembly.Services
 
 @inject LazyAssemblyLoader lazyLoader
 
@@ -31,25 +31,24 @@
 
     private async Task LoadAssemblies(string uri)
     {
-        try
+        if (uri.EndsWith("WithLazyAssembly"))
         {
-            if (uri.EndsWith("WithLazyAssembly"))
+            Console.WriteLine($"Loading assemblies for WithLazyAssembly...");
-            {
+            var assemblies = await lazyLoader.LoadAssembliesAsync(new List<string>() { "Newtonsoft.Json.dll" });
-                Console.WriteLine($"Loading assemblies for WithLazyAssembly...");
+            lazyLoadedAssemblies.AddRange(assemblies);
-                var assemblies = await lazyLoader.LoadAssembliesAsync(new List<string>() { "Newtonsoft.Json.dll" });
-                lazyLoadedAssemblies.AddRange(assemblies);
-            }
-
-            if (uri.EndsWith("WithLazyLoadedRoutes"))
-            {
-                Console.WriteLine($"Loading assemblies for WithLazyLoadedRoutes...");
-                var assemblies = await lazyLoader.LoadAssembliesAsync(new List<string>() { "LazyTestContentPackage.dll" });
-                lazyLoadedAssemblies.AddRange(assemblies);
-            }
         }
-        catch (Exception e)
+
+        if (uri.EndsWith("WithLazyLoadedRoutes"))
         {
-            Console.WriteLine($"Error when loading assemblies: {e}");
+            Console.WriteLine($"Loading assemblies for WithLazyLoadedRoutes...");
+            var assemblies = await lazyLoader.LoadAssembliesAsync(new List<string>() { "LazyTestContentPackage.dll" });
+            lazyLoadedAssemblies.AddRange(assemblies);
+        }
+
+        if (uri.EndsWith("Other")) {
+            Console.WriteLine($"Loading assemblies for Other...");
+            var assemblies = await lazyLoader.LoadAssembliesAsync(new List<string>() { "DoesNotExist.dll" });
+            lazyLoadedAssemblies.AddRange(assemblies);
         }
     }
 }

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

@@ -43,6 +43,8 @@
     </script>
     <script src="_framework/blazor.webassembly.js"></script>
 
+    <script src="_content/Microsoft.AspNetCore.Components.Web.Extensions/headManager.js"></script>
+
     <!-- Used by ExternalContentPackage -->
     <script src="_content/TestContentPackage/prompt.js"></script>
 </body>

src/Components/test/testassets/TestServer/Pages/PrerenderedHost.cshtml

@@ -19,6 +19,9 @@
     <button id="load-boot-script" onclick="start()">Load boot script</button>
 
     <script src="_framework/blazor.server.js" autostart="false"></script>
+
+    <script src="_content/Microsoft.AspNetCore.Components.Web.Extensions/headManager.js"></script>
+
     <script>
         // Used by InteropOnInitializationComponent
         function setElementValue(element, newValue) {

src/Components/test/testassets/TestServer/Pages/_ServerHost.cshtml

@@ -39,6 +39,8 @@
 
     <script src="_framework/blazor.server.js"></script>
 
+    <script src="_content/Microsoft.AspNetCore.Components.Web.Extensions/headManager.js"></script>
+
     <!-- Used by ExternalContentPackage -->
     <script src="_content/TestContentPackage/prompt.js"></script>
     <script>

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

@@ -5,7 +5,6 @@ using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.AspNetCore.Components.WebAssembly.Services;
-using Microsoft.JSInterop;
 
 namespace TestServer
 {