In SpaServices NuGet package, pass through error stack when NPM modules fail to load

Author: SteveSandersonMS

src/Microsoft.AspNetCore.SpaServices/Content/Node/prerenderer.js

@@ -4,7 +4,10 @@ module.exports.renderToString = function (callback){
 try{
 aspNetPrerendering=require('aspnet-prerendering');
 }catch(ex){
-callback('To use prerendering, you must install the \'aspnet-prerendering\' NPM package.');
+// Developers sometimes have trouble with badly-configured Node installations, where it's unable
+// to find node_modules. Or they accidentally fail to deploy node_modules, or even to run 'npm install'.
+// Make sure such errors are reported back to the .NET part of the app.
+callback('Prerendering failed because of an error while loading \'aspnet-prerendering\'. Error was: '+ex.stack);
 return;
 }
 

src/Microsoft.AspNetCore.SpaServices/Content/Node/webpack-dev-middleware.js

@@ -4,7 +4,10 @@ module.exports.createWebpackDevServer = function (callback){
 try{
 aspNetWebpack=require('aspnet-webpack');
 }catch(ex){
-callback('To use webpack dev middleware, you must install the \'aspnet-webpack\' NPM package.');
+// Developers sometimes have trouble with badly-configured Node installations, where it's unable
+// to find node_modules. Or they accidentally fail to deploy node_modules, or even to run 'npm install'.
+// Make sure such errors are reported back to the .NET part of the app.
+callback('Webpack dev middleware failed because of an error while loading \'aspnet-webpack\'. Error was: '+ex.stack);
 return;
 }