Deprecated: improve .trim for strings containing lots of whitespaces

vlsi · vlsi · commit 09bb467aaa58 · 2022-07-13T13:11:05.000+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.

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/deprecated.js b/src/deprecated.js
@@ -6,16 +6,22 @@ define( [
 	"./var/isFunction",
 	"./var/isWindow",
 	"./var/slice",
+	"./deprecated/support",
 
 	"./deprecated/ajax-event-alias",
 	"./deprecated/event"
-], function( jQuery, nodeName, camelCase, toType, isFunction, isWindow, slice ) {
+], function( jQuery, nodeName, camelCase, toType, isFunction, isWindow, slice, support ) {
 
 "use strict";
 
 // Support: Android <=4.0 only
 // Make sure we trim BOM and NBSP
-var 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.
+// It is important that non-whitespace char is mandatory for regexp performance reasons,
+// however, it does not break correctness since whitespace-only string will be trimmed by ltrim above.
+var ltrim = /^[\s\uFEFF\xA0]+/,
+	rtrim = /([^\s\uFEFF\xA0])[\s\uFEFF\xA0]+$/;
 
 // Bind a function to a context, optionally partially applying any
 // arguments.
@@ -80,8 +86,11 @@ jQuery.isNumeric = function( obj ) {
 };
 
 jQuery.trim = function( text ) {
-	return text == null ?
-		"" :
-		( text + "" ).replace( rtrim, "" );
+	if ( text == null ) {
+		return "";
+	}
+	return support.trim ?
+		( text + "" ).trim() :
+		( text + "" ).replace( ltrim, "" ).replace( rtrim, "$1" );
 };
 } );
diff --git a/src/deprecated/support.js b/src/deprecated/support.js
@@ -0,0 +1,11 @@
+define( [
+	"../var/support"
+], function( support ) {
+
+	"use strict";
+
+	support.trim = "".trim && "_" === " \uFEFF\xA0_\uFEFF\xA0 ".trim();
+
+	return support;
+
+} );
