Performance: improve .trim performance for large strings contains lots of whitespaces

vlsi · vlsi · commit f84b0ba7528f · 2022-07-20T11:58:24.000+03:00
The old implementation took O(N^2) time to trim the string when multiple adjacent spaces were present. For instance, consider the string "A B" (10 spaces between A and B). Then old regexp /[\s]+$/ would take 10 steps until it realizes the regexp does not match at position 1. Then it would try to match the regexp at position 2, and it would take 9 steps. Then 8 steps for position 3, ... so it would take 10*10/2 steps until it figures out the regexp does not match. See jquery/jquery#5068 The new approach is to require "non-whitespace" char before the whitespace run, so it spends just one step for each space in the string.
diff --git a/src/jquery/core.js b/src/jquery/core.js
@@ -15,9 +15,9 @@ var findProp,
 	rattrHashTest = /\[(\s*[-\w]+\s*)([~|^$*]?=)\s*([-\w#]*?#[-\w#]*)\s*\]/,
 	rattrHashGlob = /\[(\s*[-\w]+\s*)([~|^$*]?=)\s*([-\w#]*?#[-\w#]*)\s*\]/g,
 
-	// Support: Android <=4.0 only
-	// Make sure we trim BOM and NBSP
-	rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g;
+	// Require that the "whitespace run" starts from a non-whitespace
+	// to avoid O(N^2) behavior when the engine would try matching "\s+$" at each space position.
+	rtrim = /^[\s\uFEFF\xA0]+|([^\s\uFEFF\xA0])[\s\uFEFF\xA0]+$/g;
 
 migratePatchFunc( jQuery.fn, "init", function( arg1 ) {
 	var args = Array.prototype.slice.call( arguments );
@@ -109,7 +109,7 @@ if ( jQueryVersionSince( "3.1.1" ) ) {
 	migratePatchAndWarnFunc( jQuery, "trim", function( text ) {
 		return text == null ?
 			"" :
-			( text + "" ).replace( rtrim, "" );
+			( text + "" ).replace( rtrim, "$1" );
 	}, "trim",
 	"jQuery.trim is deprecated; use String.prototype.trim" );
 }
