[Refactor] Handle pathological strings better

implementation.js

@@ -3,6 +3,7 @@
 var RequireObjectCoercible = require('es-object-atoms/RequireObjectCoercible');
 var ToString = require('es-abstract/2024/ToString');
 var callBound = require('call-bound');
+var safeRegexTester = require('safe-regex-test');
 var $replace = callBound('String.prototype.replace');
 
 var mvsIsWS = (/^\s$/).test('\u180E');
@@ -13,9 +14,15 @@ var leftWhitespace = mvsIsWS
 var rightWhitespace = mvsIsWS
 	? /[\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF]+$/
 	: /[\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF]+$/;
+var hasRightMostWhitespace = safeRegexTester(mvsIsWS
+	? /[\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF]$/
+	: /[\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF]$/);
 /* eslint-enable no-control-regex */
 
 module.exports = function trim() {
 	var S = ToString(RequireObjectCoercible(this));
+	if (!hasRightMostWhitespace(S)) {
+		return $replace(S, leftWhitespace, '');
+	}
 	return $replace($replace(S, leftWhitespace, ''), rightWhitespace, '');
 };

package.json

@@ -52,9 +52,11 @@
 		"define-properties": "^1.2.1",
 		"es-abstract": "^1.23.5",
 		"es-object-atoms": "^1.0.0",
-		"has-property-descriptors": "^1.0.2"
+		"has-property-descriptors": "^1.0.2",
+		"safe-regex-test": "^1.1.0"
 	},
 	"devDependencies": {
+		"@ericcornelissen/assert-time": "^1.0.0",
 		"@es-shims/api": "^2.5.1",
 		"@ljharb/eslint-config": "^21.1.1",
 		"auto-changelog": "^2.5.0",
@@ -67,6 +69,7 @@
 		"npmignore": "^0.3.1",
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
+		"string.prototype.repeat": "^1.0.0",
 		"tape": "^5.9.0"
 	},
 	"testling": {

test/tests.js

@@ -1,18 +1,34 @@
 'use strict';
 
 var forEach = require('for-each');
+var repeat = require('string.prototype.repeat');
+var assertTime = require('@ericcornelissen/assert-time');
 
 module.exports = function (trim, t) {
 	t.test('normal cases', function (st) {
 		st.equal(trim(' \t\na \t\n'), 'a', 'strips whitespace off left and right sides');
 		st.equal(trim('a'), 'a', 'noop when no whitespace');
+		st.equal(trim(' a'), 'a', 'strips whitespace off left side only');
+		st.equal(trim('a '), 'a', 'strips whitespace off right side only');
 
 		var allWhitespaceChars = '\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF';
 		st.equal(trim(allWhitespaceChars + 'a' + allWhitespaceChars), 'a', 'all expected whitespace chars are trimmed');
 
 		st.end();
 	});
 
+	t.test('pathological case', function (st) {
+		var input = 'A' + repeat(' ', 100000) + 'A';
+
+		st.doesNotThrow(function () {
+			assertTime(function () {
+				trim(input);
+			}, 500);
+		});
+
+		st.end();
+	});
+
 	// see https://codeblog.jonskeet.uk/2014/12/01/when-is-an-identifier-not-an-identifier-attack-of-the-mongolian-vowel-separator/
 	var mongolianVowelSeparator = '\u180E';
 	var mvsIsWS = (/^\s$/).test('\u180E');