mediawiki.user: Small perf tweak for generateRandomSessionId

Consolidate loop + join into explicit string concatenation

Bug: T201124
Change-Id: Ie7c7ddd29783ada142fbb7b726caa697048802f3

diff --git a/resources/src/mediawiki.user.js b/resources/src/mediawiki.user.js
index bf23da1..251b108 100644 (file)
--- a/resources/src/mediawiki.user.js
+++ b/resources/src/mediawiki.user.js
@@ -46,35 +46,31 @@
                 */
                generateRandomSessionId: function () {
                        var rnds, i,
-                               hexRnds = new Array( 5 ),
                                // Support: IE 11
                                crypto = window.crypto || window.msCrypto;
 
                        if ( crypto && crypto.getRandomValues && typeof Uint16Array === 'function' ) {
-
                                // Fill an array with 5 random values, each of which is 16 bits.
                                // Note that Uint16Array is array-like but does not implement Array.
                                rnds = new Uint16Array( 5 );
                                crypto.getRandomValues( rnds );
-
                        } else {
-
                                // 0x10000 is 2^16 so the operation below will return a number
                                // between 2^16 and zero
                                for ( i = 0; i < 5; i++ ) {
                                        rnds[ i ] = Math.floor( Math.random() * 0x10000 );
                                }
                        }
-                       // Convert the 5 16bit-numbers into 20 characters (4 hex chars per 16 bits)
-                       for ( i = 0; i < 5; i++ ) {
-                               // Add 0x1000 before converting to hex and strip the extra character
-                               // after converting to keep the leading zeros.
-                               hexRnds[ i ] = ( rnds[ i ] + 0x10000 ).toString( 16 ).slice( 1 );
-                       }
 
+                       // Convert the 5 16bit-numbers into 20 characters (4 hex per 16 bits).
                        // Concatenation of two random integers with entropy n and m
-                       // returns a string with entropy n+m if those strings are independent
-                       return hexRnds.join( '' );
+                       // returns a string with entropy n+m if those strings are independent.
+                       // Tested that below code is faster than array + loop + join.
+                       return ( rnds[ 0 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+                               ( rnds[ 1 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+                               ( rnds[ 2 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+                               ( rnds[ 3 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+                               ( rnds[ 4 ] + 0x10000 ).toString( 16 ).slice( 1 );
                },
 
                /**