Remove System.Runtime.Loader dependency to enable net461 support. Use IApplicationLifetime instead of AssemblyLoadContext.Default.Unloading.

src/Microsoft.AspNetCore.SpaServices/Prerendering/PrerenderTagHelper.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http.Features;
@@ -24,6 +25,7 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
         private static INodeServices _fallbackNodeServices; // Used only if no INodeServices was registered with DI
 
         private readonly string _applicationBasePath;
+        private readonly CancellationToken _applicationStoppingToken;
         private readonly INodeServices _nodeServices;
 
         /// <summary>
@@ -35,6 +37,9 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
             var hostEnv = (IHostingEnvironment) serviceProvider.GetService(typeof(IHostingEnvironment));
             _nodeServices = (INodeServices) serviceProvider.GetService(typeof(INodeServices)) ?? _fallbackNodeServices;
             _applicationBasePath = hostEnv.ContentRootPath;
+            
+            var applicationLifetime = (IApplicationLifetime) serviceProvider.GetService(typeof(IApplicationLifetime));
+            _applicationStoppingToken = applicationLifetime.ApplicationStopping;
 
             // Consider removing the following. Having it means you can get away with not putting app.AddNodeServices()
             // in your startup file, but then again it might be confusing that you don't need to.
@@ -101,6 +106,7 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
             var result = await Prerenderer.RenderToString(
                 _applicationBasePath,
                 _nodeServices,
+                _applicationStoppingToken,
                 new JavaScriptModuleExport(ModuleName)
                 {
                     ExportName = ExportName

src/Microsoft.AspNetCore.SpaServices/Prerendering/Prerenderer.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.NodeServices;
 
@@ -9,22 +10,16 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
     /// </summary>
     public static class Prerenderer
     {
-        private static readonly Lazy<StringAsTempFile> NodeScript;
+        private static readonly object CreateNodeScriptLock = new object();
 
-        static Prerenderer()
-        {
-            NodeScript = new Lazy<StringAsTempFile>(() =>
-            {
-                var script = EmbeddedResourceReader.Read(typeof(Prerenderer), "/Content/Node/prerenderer.js");
-                return new StringAsTempFile(script); // Will be cleaned up on process exit
-            });
-        }
+        private static StringAsTempFile NodeScript;
 
         /// <summary>
         /// Performs server-side prerendering by invoking code in Node.js.
         /// </summary>
         /// <param name="applicationBasePath">The root path to your application. This is used when resolving project-relative paths.</param>
         /// <param name="nodeServices">The instance of <see cref="INodeServices"/> that will be used to invoke JavaScript code.</param>
+        /// <param name="applicationStoppingToken">A token that indicates when the host application is stopping.</param>
         /// <param name="bootModule">The path to the JavaScript file containing the prerendering logic.</param>
         /// <param name="requestAbsoluteUrl">The URL of the currently-executing HTTP request. This is supplied to the prerendering code.</param>
         /// <param name="requestPathAndQuery">The path and query part of the URL of the currently-executing HTTP request. This is supplied to the prerendering code.</param>
@@ -35,6 +30,7 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
         public static Task<RenderToStringResult> RenderToString(
             string applicationBasePath,
             INodeServices nodeServices,
+            CancellationToken applicationStoppingToken,
             JavaScriptModuleExport bootModule,
             string requestAbsoluteUrl,
             string requestPathAndQuery,
@@ -43,7 +39,7 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
             string requestPathBase)
         {
             return nodeServices.InvokeExportAsync<RenderToStringResult>(
-                NodeScript.Value.FileName,
+                GetNodeScriptFilename(applicationStoppingToken),
                 "renderToString",
                 applicationBasePath,
                 bootModule,
@@ -53,5 +49,19 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
                 timeoutMilliseconds,
                 requestPathBase);
         }
+
+        private static string GetNodeScriptFilename(CancellationToken applicationStoppingToken)
+        {
+            lock(CreateNodeScriptLock)
+            {
+                if (NodeScript == null)
+                {
+                    var script = EmbeddedResourceReader.Read(typeof(Prerenderer), "/Content/Node/prerenderer.js");
+                    NodeScript = new StringAsTempFile(script, applicationStoppingToken); // Will be cleaned up on process exit
+                }
+            }
+
+            return NodeScript.FileName;
+        }
     }
 }

src/Microsoft.AspNetCore.SpaServices/Webpack/WebpackDevMiddleware.cs

@@ -68,7 +68,7 @@ namespace Microsoft.AspNetCore.Builder
             // Get a filename matching the middleware Node script
             var script = EmbeddedResourceReader.Read(typeof(WebpackDevMiddleware),
                 "/Content/Node/webpack-dev-middleware.js");
-            var nodeScript = new StringAsTempFile(script); // Will be cleaned up on process exit
+            var nodeScript = new StringAsTempFile(script, nodeServicesOptions.ApplicationStoppingToken); // Will be cleaned up on process exit
 
             // Ideally, this would be relative to the application's PathBase (so it could work in virtual directories)
             // but it's not clear that such information exists during application startup, as opposed to within the context