fs: rename event to eventType in fs.watch listener

The name 'event' for the argument of the listener in
fs.watch was confusing considering FSWatcher also had
events. This changes the name of the argument to
eventType.

Fixes: nodejs#7504
PR-URL: nodejs#7506
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

doc/api/fs.md

@@ -109,14 +109,19 @@ non-UTF-8 encoded Buffers to `fs` functions will not work as expected.
 added: v0.5.8
 -->
 
-Objects returned from `fs.watch()` are of this type.
+Objects returned from [`fs.watch()`][] are of this type.
+
+The `listener` callback provided to `fs.watch()` receives the returned FSWatcher's
+`change` events.
+
+The object itself emits these events:
 
 ### Event: 'change'
 <!-- YAML
 added: v0.5.8
 -->
 
-* `event` {String} The type of fs change
+* `eventType` {String} The type of fs change
 * `filename` {String | Buffer} The filename that changed (if relevant/available)
 
 Emitted when something changes in a watched directory or file.
@@ -128,7 +133,8 @@ support. If `filename` is provided, it will be provided as a `Buffer` if
 `filename` will be a string.
 
 ```js
-fs.watch('./tmp', {encoding: 'buffer'}, (event, filename) => {
+// Example when handled through fs.watch listener
+fs.watch('./tmp', {encoding: 'buffer'}, (eventType, filename) => {
   if (filename)
     console.log(filename);
     // Prints: <Buffer ...>
@@ -1443,10 +1449,13 @@ directory.  The returned object is a [`fs.FSWatcher`][].
 The second argument is optional. If `options` is provided as a string, it
 specifies the `encoding`. Otherwise `options` should be passed as an object.
 
-The listener callback gets two arguments `(event, filename)`.  `event` is either
+The listener callback gets two arguments `(eventType, filename)`.  `eventType` is either
 `'rename'` or `'change'`, and `filename` is the name of the file which triggered
 the event.
 
+Please note the listener callback is attached to the `'change'` event
+fired by [`fs.FSWatcher`][], but they are not the same thing.
+
 ### Caveats
 
 <!--type=misc-->
@@ -1499,8 +1508,8 @@ be provided. Therefore, don't assume that `filename` argument is always
 provided in the callback, and have some fallback logic if it is null.
 
 ```js
-fs.watch('somedir', (event, filename) => {
-  console.log(`event is: ${event}`);
+fs.watch('somedir', (eventType, filename) => {
+  console.log(`event type is: ${eventType}`);
   if (filename) {
     console.log(`filename provided: ${filename}`);
   } else {

lib/fs.js

@@ -1399,7 +1399,7 @@ function FSWatcher() {
   this._handle = new FSEvent();
   this._handle.owner = this;
 
-  this._handle.onchange = function(status, event, filename) {
+  this._handle.onchange = function(status, eventType, filename) {
     if (status < 0) {
       self._handle.close();
       const error = !filename ?
@@ -1409,7 +1409,7 @@ function FSWatcher() {
       error.filename = filename;
       self.emit('error', error);
     } else {
-      self.emit('change', event, filename);
+      self.emit('change', eventType, filename);
     }
   };
 }