add special case for async without name

lib/optimize/CommonsChunkPlugin.js

@@ -115,7 +115,18 @@ You can however specify the name of the async chunk by passing the desired strin
 					// override the "commonChunk" with the newly created async one and use it as commonChunk from now on
 					let asyncChunk;
 					if(this.async) {
-						asyncChunk = this.createAsyncChunk(compilation, this.async, targetChunk);
+						// If async chunk is one of the affected chunks, just use it
+						asyncChunk = affectedChunks.filter(c => c.name === this.async)[0];
+						// Elsewise create a new one
+						if(!asyncChunk) {
+							asyncChunk = this.createAsyncChunk(
+								compilation,
+								targetChunks.length <= 1 || typeof this.async !== "string" ? this.async :
+								targetChunk.name ? `${this.async}-${targetChunk.name}` :
+								true,
+								targetChunk
+							);
+						}
 						targetChunk = asyncChunk;
 					}
 
@@ -306,7 +317,7 @@ Take a look at the "name"/"names" or async/children option.`);
 
 	extractModulesAndReturnAffectedChunks(reallyUsedModules, usedChunks) {
 		return reallyUsedModules.reduce((affectedChunksSet, module) => {
-			for(let chunk of usedChunks) {
+			for(const chunk of usedChunks) {
 				// removeChunk returns true if the chunk was contained and succesfully removed
 				// false if the module did not have a connection to the chunk in question
 				if(module.removeChunk(chunk)) {
@@ -318,28 +329,29 @@ Take a look at the "name"/"names" or async/children option.`);
 	}
 
 	addExtractedModulesToTargetChunk(chunk, modules) {
-		for(let module of modules) {
+		for(const module of modules) {
 			chunk.addModule(module);
 			module.addChunk(chunk);
 		}
 	}
 
 	makeTargetChunkParentOfAffectedChunks(usedChunks, commonChunk) {
-		for(let chunk of usedChunks) {
+		for(const chunk of usedChunks) {
 			// set commonChunk as new sole parent
 			chunk.parents = [commonChunk];
 			// add chunk to commonChunk
 			commonChunk.addChunk(chunk);
 
-			for(let entrypoint of chunk.entrypoints) {
+			for(const entrypoint of chunk.entrypoints) {
 				entrypoint.insertChunk(commonChunk, chunk);
 			}
 		}
 	}
 
 	moveExtractedChunkBlocksToTargetChunk(chunks, targetChunk) {
-		for(let chunk of chunks) {
-			for(let block of chunk.blocks) {
+		for(const chunk of chunks) {
+			if(chunk === targetChunk) continue;
+			for(const block of chunk.blocks) {
 				if(block.chunks.indexOf(targetChunk) === -1) {
 					block.chunks.unshift(targetChunk);
 				}
@@ -350,8 +362,8 @@ Take a look at the "name"/"names" or async/children option.`);
 
 	extractOriginsOfChunksWithExtractedModules(chunks) {
 		const origins = [];
-		for(let chunk of chunks) {
-			for(let origin of chunk.origins) {
+		for(const chunk of chunks) {
+			for(const origin of chunk.origins) {
 				const newOrigin = Object.create(origin);
 				newOrigin.reasons = (origin.reasons || []).concat("async commons");
 				origins.push(newOrigin);