ResourceLoader: Remove unused 'thisValue' from mw.trackSubscribe

This exposed the internal queue structure, which thus means that
future changes to this structure are noticable through the public
interface (mw.trackSubscribe callbacks). Those callbacks could rely
on the presence of a specific property, or perhaps modify or merge
it with something else, and thus also rely on the absence of certain
properties that they added themselves before or after that merge.

Avoid this by removing support for it.

It was introduced in 2013 with I8c7af097e6 (873b60f194), but never
used:

https://codesearch.wmcloud.org/deployed/?q=mw.trackSubscribe%7Cthis%5C.topic%5Cb&files=js%24&excludeFiles=test%7Cnode_modules

Change-Id: I2d9bc9b7228ab5f2df2160181f41c40cce8f42b6

1 files changed, 4 insertions, 5 deletions

diff --git a/resources/src/mediawiki.base/mediawiki.base.js b/resources/src/mediawiki.base/mediawiki.base.js
index fee7ecddd302..c72f79e5d11f 100644
--- a/resources/src/mediawiki.base/mediawiki.base.js
+++ b/resources/src/mediawiki.base/mediawiki.base.js
@@ -390,9 +390,8 @@ mw.track = function ( topic, data ) {
  * Register a handler for subset of analytic events, specified by topic.
  *
  * Handlers will be called once for each tracked event, including for any buffered events that
- * fired before the handler was subscribed. The callback is passed a `topic` string, and optional
- * `data` event object. The `this` value for the callback is a plain object with `topic` and
- * `data` properties set to those same values.
+ * fired before the handler was subscribed. The callback is passed a `topic` string, and an optional
+ * `data` argument.
  *
  * @example
  * // To monitor all topics for debugging
@@ -406,7 +405,7 @@ mw.track = function ( topic, data ) {
  * @param {string} topic Handle events whose name starts with this string prefix
  * @param {Function} callback Handler to call for each matching tracked event
  * @param {string} callback.topic
- * @param {Object} [callback.data]
+ * @param {Object|number|string} [callback.data]
  */
 mw.trackSubscribe = function ( topic, callback ) {
 	let seen = 0;
@@ -414,7 +413,7 @@ mw.trackSubscribe = function ( topic, callback ) {
 		for ( ; seen < trackQueue.length; seen++ ) {
 			const event = trackQueue[ seen ];
 			if ( event.topic.indexOf( topic ) === 0 ) {
-				callback.call( event, event.topic, event.data );
+				callback( event.topic, event.data );
 			}
 		}
 	}