In Webpack dev middleware, for configs that target Node, just run a 'watch' compiler (since Node isn't going to fetch the modules via HTTP anyway)

Author: SteveSandersonMS

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-webpack/src/WebpackDevMiddleware.ts

@@ -43,7 +43,7 @@ function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configurati
 }
 });
 
-webpackConfig.plugins=webpackConfig.plugins||[];
+webpackConfig.plugins=[].concat(webpackConfig.plugins||[]);// Be sure not to mutate the original array, as it might be shared
 webpackConfig.plugins.push(
 newwebpack.HotModuleReplacementPlugin()
 );
@@ -79,6 +79,13 @@ function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configurati
 }
 }
 
+functionbeginWebpackWatcher(webpackConfig: webpack.Configuration){
+constcompiler=webpack(webpackConfig);
+compiler.watch({/* watchOptions */},(err,stats)=>{
+// The default error reporter is fine for now, but could be customized here in the future if desired
+});
+}
+
 exportfunctioncreateWebpackDevServer(callback: CreateDevServerCallback,optionsJson: string){
 constoptions: CreateDevServerOptions=JSON.parse(optionsJson);
 
@@ -93,15 +100,6 @@ export function createWebpackDevServer(callback: CreateDevServerCallback, option
 webpackConfigArray=[webpackConfigArrayaswebpack.Configuration];
 }
 
-// Check that at least one of the configurations specifies a publicPath. Those are the only ones we'll
-// enable middleware for, and if there aren't any, you must be making a mistake.
-constwebpackConfigsWithPublicPath=webpackConfigArray
-.filter(webpackConfig=>(webpackConfig.output.publicPath||'').trim()!=='');
-if(webpackConfigsWithPublicPath.length===0){
-callback('To use the Webpack dev server, you must specify a value for \'publicPath\' on the \'output\' section of your webpack.config.',null);
-return;
-}
-
 constenableHotModuleReplacement=options.suppliedOptions.HotModuleReplacement;
 constenableReactHotModuleReplacement=options.suppliedOptions.ReactHotModuleReplacement;
 if(enableReactHotModuleReplacement&&!enableHotModuleReplacement){
@@ -116,16 +114,30 @@ export function createWebpackDevServer(callback: CreateDevServerCallback, option
 constlistener=app.listen(suggestedHMRPortOrZero,()=>{
 try{
 // For each webpack config that specifies a public path, add webpack dev middleware for it
-webpackConfigsWithPublicPath.forEach(webpackConfig=>{
-attachWebpackDevMiddleware(app,webpackConfig,enableHotModuleReplacement,enableReactHotModuleReplacement);
+constnormalizedPublicPaths: string[]=[];
+webpackConfigArray.forEach(webpackConfig=>{
+if(webpackConfig.target==='node'){
+// For configs that target Node, it's meaningless to set up an HTTP listener, since
+// Node isn't going to load those modules over HTTP anyway. It just loads them directly
+// from disk. So the most relevant thing we can do with such configs is just write
+// updated builds to disk, just like "webpack --watch".
+beginWebpackWatcher(webpackConfig);
+}else{
+// For configs that target browsers, we can set up an HTTP listener, and dynamically
+// modify the config to enable HMR etc. This just requires that we have a publicPath.
+constpublicPath=(webpackConfig.output.publicPath||'').trim();
+if(!publicPath){
+thrownewError('To use the Webpack dev server, you must specify a value for \'publicPath\' on the \'output\' section of your webpack config (for any configuration that targets browsers)');
+}
+normalizedPublicPaths.push(removeTrailingSlash(publicPath));
+attachWebpackDevMiddleware(app,webpackConfig,enableHotModuleReplacement,enableReactHotModuleReplacement);
+}
 });
 
 // Tell the ASP.NET app what addresses we're listening on, so that it can proxy requests here
 callback(null,{
 Port: listener.address().port,
-PublicPaths: webpackConfigsWithPublicPath.map(webpackConfig=>
-removeTrailingSlash(getPath(webpackConfig.output.publicPath))
-)
+PublicPaths: normalizedPublicPaths
 });
 }catch(ex){
 callback(ex.stack,null);