Merge pull request #3103 from kutyel/master

Add callback to Watching.prototype.invalidate

lib/Compiler.js

@@ -19,6 +19,7 @@ class Watching {
 		this.startTime = null;
 		this.invalid = false;
 		this.handler = handler;
+		this.callbacks = [];
 		this.closed = false;
 		if(typeof watchOptions === "number") {
 			this.watchOptions = {
@@ -105,6 +106,8 @@ class Watching {
 		if(!this.closed) {
 			this.watch(compilation.fileDependencies, compilation.contextDependencies, compilation.missingDependencies);
 		}
+		this.callbacks.forEach(cb => cb());
+		this.callbacks.length = 0;
 	}
 
 	watch(files, dirs, missing) {
@@ -122,7 +125,10 @@ class Watching {
 		});
 	}
 
-	invalidate() {
+	invalidate(callback) {
+		if(callback) {
+			this.callbacks.push(callback);
+		}
 		if(this.watcher) {
 			this.pausedWatcher = this.watcher;
 			this.watcher.pause();