Improve HMR error handling webpack#410

Author: sokra

lib/JsonpMainTemplatePlugin.js

@@ -157,20 +157,30 @@ JsonpMainTemplatePlugin.prototype.apply = function(mainTemplate) {
 					return callback(new Error("No browser support"));
 				try {
 					var request = new XMLHttpRequest();
-					request.open("GET", $require$.p + $hotMainFilename$, true);
+					var requestPath = $require$.p + $hotMainFilename$;
+					request.open("GET", requestPath, true);
+					request.timeout = 10000;
 					request.send(null);
 				} catch(err) {
 					return callback(err);
 				}
 				request.onreadystatechange = function() {
 					if(request.readyState !== 4) return;
-					if(request.status !== 200 && request.status !== 304) {
+					if(request.status === 0) {
+						// timeout
+						callback(new Error("Manifest request to " + requestPath + " timed out."));
+					} else if(request.status === 404) {
+						// no update available
 						callback();
+					} else if(request.status !== 200 && request.status !== 304) {
+						// other failure
+						callback(new Error("Manifest request to " + requestPath + " failed."));
 					} else {
+						// success
 						try {
 							var update = JSON.parse(request.responseText);
 						} catch(e) {
-							callback();
+							callback(e);
 							return;
 						}
 						callback(null, update);