WebpackDevMiddleware should run in a separate Node instance that doesn't restart when files change (otherwise there's no point in running it at all)

src/Microsoft.AspNet.NodeServices/Configuration.cs

@@ -3,24 +3,40 @@ using Microsoft.Extensions.PlatformAbstractions;
 
 namespace Microsoft.AspNet.NodeServices {
     public static class Configuration {
-        public static void AddNodeServices(this IServiceCollection serviceCollection, NodeHostingModel hostingModel = NodeHostingModel.Http) {
+        private static string[] defaultWatchFileExtensions = new[] { ".js", ".jsx", ".ts", ".tsx", ".json", ".html" };
+        
+        public static void AddNodeServices(this IServiceCollection serviceCollection, NodeServicesOptions options) {
             serviceCollection.AddSingleton(typeof(INodeServices), (serviceProvider) => {
                 var appEnv = serviceProvider.GetRequiredService<IApplicationEnvironment>();
-                return CreateNodeServices(hostingModel, appEnv.ApplicationBasePath);
+                if (string.IsNullOrEmpty(options.ProjectPath)) {
+                    options.ProjectPath = appEnv.ApplicationBasePath;
+                }
+                return CreateNodeServices(options);
             });
         }
 
-        public static INodeServices CreateNodeServices(NodeHostingModel hostingModel, string projectPath)
+        public static INodeServices CreateNodeServices(NodeServicesOptions options)
         {
-            switch (hostingModel)
+            var watchFileExtensions = options.WatchFileExtensions ?? defaultWatchFileExtensions;
+            switch (options.HostingModel)
             {
                 case NodeHostingModel.Http:
-                    return new HttpNodeInstance(projectPath);
+                    return new HttpNodeInstance(options.ProjectPath, /* port */ 0, watchFileExtensions);
                 case NodeHostingModel.InputOutputStream:
-                    return new InputOutputStreamNodeInstance(projectPath);
+                    return new InputOutputStreamNodeInstance(options.ProjectPath);
                 default:
-                    throw new System.ArgumentException("Unknown hosting model: " + hostingModel.ToString());
+                    throw new System.ArgumentException("Unknown hosting model: " + options.HostingModel.ToString());
             }
         }
     }
+
+    public class NodeServicesOptions {
+        public NodeHostingModel HostingModel { get; set; }
+        public string ProjectPath { get; set; }
+        public string[] WatchFileExtensions { get; set; }
+        
+        public NodeServicesOptions() {
+            this.HostingModel = NodeHostingModel.Http;
+        }
+    }
 }

src/Microsoft.AspNet.NodeServices/Content/Node/entrypoint-http.js

@@ -2,9 +2,12 @@
 // but simplifies things for the consumer of this module.
 var http = require('http');
 var path = require('path');
-var requestedPortOrZero = parseInt(process.argv[2]) || 0; // 0 means 'let the OS decide'
+var parsedArgs = parseArgs(process.argv);
+var requestedPortOrZero = parsedArgs.port || 0; // 0 means 'let the OS decide'
 
-autoQuitOnFileChange(process.cwd(), ['.js', '.jsx', '.ts', '.tsx', '.json', '.html']);
+if (parsedArgs.watch) {
+    autoQuitOnFileChange(process.cwd(), parsedArgs.watch.split(','));
+}
 
 var server = http.createServer(function(req, res) {
     readRequestBodyAsJson(req, function(bodyJson) {
@@ -75,3 +78,22 @@ function autoQuitOnFileChange(rootDir, extensions) {
         }
     });
 }
+
+function parseArgs(args) {
+    // Very simplistic parsing which is sufficient for the cases needed. We don't want to bring in any external
+    // dependencies (such as an args-parsing library) to this file.
+    var result = {};
+    var currentKey = null;
+    args.forEach(function(arg) {
+        if (arg.indexOf('--') === 0) {
+            var argName = arg.substring(2);
+            result[argName] = undefined;
+            currentKey = argName;
+        } else if (currentKey) {
+            result[currentKey] = arg;
+            currentKey = null;
+        }
+    });
+
+    return result;
+}

src/Microsoft.AspNet.NodeServices/HostingModels/HttpNodeInstance.cs

@@ -17,11 +17,19 @@ namespace Microsoft.AspNet.NodeServices {
         
         private int _portNumber;
 		
-		public HttpNodeInstance(string projectPath, int port = 0)
-            : base(EmbeddedResourceReader.Read(typeof(HttpNodeInstance), "/Content/Node/entrypoint-http.js"), projectPath, port.ToString())
+		public HttpNodeInstance(string projectPath, int port = 0, string[] watchFileExtensions = null)
+            : base(EmbeddedResourceReader.Read(typeof(HttpNodeInstance), "/Content/Node/entrypoint-http.js"), projectPath, MakeCommandLineOptions(port, watchFileExtensions))
         {
 		}
         
+        private static string MakeCommandLineOptions(int port, string[] watchFileExtensions) {
+            var result = "--port " + port.ToString();
+            if (watchFileExtensions != null && watchFileExtensions.Length > 0) {
+                result += " --watch " + string.Join(",", watchFileExtensions);
+            } 
+            return result;
+        }
+        
         public override async Task<T> Invoke<T>(NodeInvocationInfo invocationInfo) {
             await this.EnsureReady();