resourceloader: Optimise several map-like objects with Object.create(null)

Object.create(null) is specifically for the use case of being
able to store any key/value without worrying about inherited
built-in methods.

As such, using Object.create(null) in these cases has two benefits:

* Removes the need for a hasOwn() call.
  One can instead use the 'in' operator, or look for undefined,
  without there being gotchas due to inherited methods.

* When the known values are always truthy (e.g. when only storing
  value that are also objects or arrays), there is no need for
  any explicit comparison (plain boolean evaluation).

Change-Id: I24f86f9938e4f5ccca81d15aa14a48ac3ddee341

diff --git a/resources/src/startup/mediawiki.js b/resources/src/startup/mediawiki.js
index 6ed226c..adde3ee 100644 (file)
--- a/resources/src/startup/mediawiki.js
+++ b/resources/src/startup/mediawiki.js
@@ -1450,7 +1450,7 @@
                         * @param {string[]} batch
                         */
                        function batchRequest( batch ) {
-                               var reqBase, splits, maxQueryLength, b, bSource, bGroup, bSourceGroup,
+                               var reqBase, splits, maxQueryLength, b, bSource, bGroup,
                                        source, group, i, modules, sourceLoadScript,
                                        currReqBase, currReqBaseLength, moduleMap, currReqModules, l,
                                        lastDotIndex, prefix, suffix, bytesAdded;
@@ -1492,22 +1492,20 @@
                                maxQueryLength = mw.config.get( 'wgResourceLoaderMaxQueryLength', 2000 );
 
                                // Split module list by source and by group.
-                               splits = {};
+                               splits = Object.create( null );
                                for ( b = 0; b < batch.length; b++ ) {
                                        bSource = registry[ batch[ b ] ].source;
                                        bGroup = registry[ batch[ b ] ].group;
-                                       if ( !hasOwn.call( splits, bSource ) ) {
-                                               splits[ bSource ] = {};
+                                       if ( !splits[ bSource ] ) {
+                                               splits[ bSource ] = Object.create( null );
                                        }
-                                       if ( !hasOwn.call( splits[ bSource ], bGroup ) ) {
+                                       if ( !splits[ bSource ][ bGroup ] ) {
                                                splits[ bSource ][ bGroup ] = [];
                                        }
-                                       bSourceGroup = splits[ bSource ][ bGroup ];
-                                       bSourceGroup.push( batch[ b ] );
+                                       splits[ bSource ][ bGroup ].push( batch[ b ] );
                                }
 
                                for ( source in splits ) {
-
                                        sourceLoadScript = sources[ source ];
 
                                        for ( group in splits[ source ] ) {
@@ -1533,7 +1531,7 @@
                                                // We may need to split up the request to honor the query string length limit,
                                                // so build it piece by piece.
                                                l = currReqBaseLength;
-                                               moduleMap = {}; // { prefix: [ suffixes ] }
+                                               moduleMap = Object.create( null ); // { prefix: [ suffixes ] }
                                                currReqModules = [];
 
                                                for ( i = 0; i < modules.length; i++ ) {
@@ -1542,7 +1540,7 @@
                                                        // If lastDotIndex is -1, substr() returns an empty string
                                                        prefix = modules[ i ].substr( 0, lastDotIndex );
                                                        suffix = modules[ i ].slice( lastDotIndex + 1 );
-                                                       bytesAdded = hasOwn.call( moduleMap, prefix ) ?
+                                                       bytesAdded = moduleMap[ prefix ] ?
                                                                suffix.length + 3 : // '%2C'.length == 3
                                                                modules[ i ].length + 3; // '%7C'.length == 3
 
@@ -1552,12 +1550,12 @@
                                                                doRequest();
                                                                // .. and start again.
                                                                l = currReqBaseLength;
-                                                               moduleMap = {};
+                                                               moduleMap = Object.create( null );
                                                                currReqModules = [];
 
                                                                mw.track( 'resourceloader.splitRequest', { maxQueryLength: maxQueryLength } );
                                                        }
-                                                       if ( !hasOwn.call( moduleMap, prefix ) ) {
+                                                       if ( !moduleMap[ prefix ] ) {
                                                                moduleMap[ prefix ] = [];
                                                        }
                                                        l += bytesAdded;