feat: support hot module replacement (HMR)

hotModuleReplacement.js

@@ -0,0 +1,19 @@
+module.exports = function(compilationHash, publicPath, outputFilename) {
+  if (document) {
+    var origin = document.location.protocol + '//' + document.location.hostname + (document.location.port ? ':' + document.location.port: '');
+    var styleSheets = document.getElementsByTagName('link');
+    for (var i = 0; i < styleSheets.length; i++) {
+      if (styleSheets[i].href) {
+        var hrefUrl = styleSheets[i].href.split('?');
+        var href = hrefUrl[0];
+        var hash = hrefUrl[1];
+        if (hash !== compilationHash && href === origin + publicPath + outputFilename) {
+          var url = href + '?' + compilationHash;
+          styleSheets[i].href = url;
+          console.log('[HMR]', 'Reload css: ', url);
+          break;
+        }
+      }
+    }
+  }
+}

index.js

@@ -22,6 +22,13 @@ function ExtractTextPluginCompilation() {
 }
 
 ExtractTextPlugin.prototype.mergeNonInitialChunks = function(chunk, intoChunk, checkedChunks) {
+	if (chunk.chunks) {
+		// Fix error when hot module replacement used with CommonsChunkPlugin
+		chunk.chunks = chunk.chunks.filter(function(c) {
+			return typeof c !== 'undefined';
+		})
+	}
+
 	if(!intoChunk) {
 		checkedChunks = [];
 		chunk.chunks.forEach(function(c) {
@@ -313,7 +320,8 @@ ExtractTextPlugin.prototype.apply = function(compiler) {
 				callback();
 			}.bind(this));
 		}.bind(this));
-		compilation.plugin("additional-assets", function(callback) {
+		compilation.plugin("before-chunk-assets", function() {
+			// This appears to be the latest hook where the %%extracted-file%% and hash replacements work on initial load. Any later and the contents of modules appears to be sealed and changes don't have any effect until the next hot update.
 			extractedChunks.forEach(function(extractedChunk) {
 				if(extractedChunk.modules.length) {
 					extractedChunk.modules.sort(function(a, b) {
@@ -336,9 +344,15 @@ ExtractTextPlugin.prototype.apply = function(compiler) {
 
 					compilation.assets[file] = source;
 					chunk.files.push(file);
+
+					// Hot module replacement
+					extractedChunk.modules.forEach(function(module){
+						var originalModule = module.getOriginalModule();
+						originalModule._source._value = originalModule._source._value.replace('%%extracted-file%%', file);
+						originalModule._source._value = originalModule._source._value.replace('%%extracted-hash%%', compilation.hash);
+					});
 				}
 			}, this);
-			callback();
 		}.bind(this));
 	}.bind(this));
 };

loader.js

@@ -10,11 +10,13 @@ var LibraryTemplatePlugin = require("webpack/lib/LibraryTemplatePlugin");
 var SingleEntryPlugin = require("webpack/lib/SingleEntryPlugin");
 var LimitChunkCountPlugin = require("webpack/lib/optimize/LimitChunkCountPlugin");
 
+var extractTextPluginHmrRuntime = require.resolve("./hotModuleReplacement.js");
 var NS = fs.realpathSync(__dirname);
 
 module.exports = function(source) {
 	if(this.cacheable) this.cacheable();
-	return source;
+	// Even though this gets overwritten if extract+remove are true, without it, the runtime doesn't get added to the chunk
+	return `if (module.hot) { require('${extractTextPluginHmrRuntime}'); }\n${source}`;
 };
 
 module.exports.pitch = function(request) {
@@ -120,8 +122,18 @@ module.exports.pitch = function(request) {
 					});
 				});
 				this[NS](text, query);
-				if(text.locals && typeof resultSource !== "undefined") {
-					resultSource += "\nmodule.exports = " + JSON.stringify(text.locals) + ";";
+				if(typeof resultSource !== "undefined") {
+					if (text.locals) {
+						resultSource += "\nmodule.exports = " + JSON.stringify(text.locals) + ";";
+					}
+					// module.hot.data is undefined on initial load, and an object in hot updates
+					resultSource += `
+if (module.hot) {
+	module.hot.accept();
+	if (module.hot.data) {
+		require('${extractTextPluginHmrRuntime}')('%%extracted-hash%%','${publicPath}','%%extracted-file%%');
+	}
+}`;
 				}
 			} catch(e) {
 				return callback(e);