fs: make unwatchFile() remove a specific listener

Before this commit, `fs.unwatchFile(path)` removed *all* listeners for `path`.

The function is overloaded now: `fs.unwatchFile(path)` still removes all
listeners, but `fs.unwatchFile(path, cb)` lets you remove a specific listener.

Fixes #3660.

1 files changed, 12 insertions, 4 deletions

diff --git a/lib/fs.js b/lib/fs.js
index 7c622375e..ae9cdf4c4 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -943,10 +943,18 @@ fs.watchFile = function(filename) {
   return stat;
 };
 
-fs.unwatchFile = function(filename) {
-  var stat;
-  if (inStatWatchers(filename)) {
-    stat = statWatchers[filename];
+fs.unwatchFile = function(filename, listener) {
+  if (!inStatWatchers(filename)) return;
+
+  var stat = statWatchers[filename];
+
+  if (typeof listener === 'function') {
+    stat.removeListener('change', listener);
+  } else {
+    stat.removeAllListeners('change');
+  }
+
+  if (stat.listeners('change').length === 0) {
     stat.stop();
     statWatchers[filename] = undefined;
   }