From 1d70b25b432e01ce52d40045b9b0a4bdb68bf2f2 Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben.bridgewater@datadoghq.com>
Date: Sat, 29 Aug 2026 02:15:36 +0200
Subject: [PATCH] perf: skip class checks for unrelated identifiers
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On a 3,629,072-code-unit corpus, seven alternating trials improved parse time from 13,161.06 to 12,783.68 µs on Node 24.20.0 (V8 13.6).

A fresh process measured 13,399.06 to 13,041.79 µs.
---
 lexer.js      |  3 ++-
 test/_unit.js | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/lexer.js b/lexer.js
index 1614fd9..aa06c38 100755
--- a/lexer.js
+++ b/lexer.js
@@ -158,7 +158,8 @@ function parseSource (cjsSource) {
         }
         break;
       case 99/*c*/:
-        if (keywordStart(pos) && source.startsWith('lass', pos + 1) && isBrOrWs(source.charCodeAt(pos + 5)))
+        if (source.charCodeAt(pos + 1) === 108/*l*/ && keywordStart(pos) &&
+            source.startsWith('ass', pos + 2) && isBrOrWs(source.charCodeAt(pos + 5)))
           nextBraceIsClass = true;
         break;
       case 109/*m*/:
diff --git a/test/_unit.js b/test/_unit.js
index 0458f17..fdf9996 100755
--- a/test/_unit.js
+++ b/test/_unit.js
@@ -478,6 +478,23 @@ suite('Lexer', () => {
     `);
   });
 
+  test('Class keyword detection', () => {
+    for (const whitespace of ['\t', '\n', '\v', '\f', '\r', ' ', '\u00a0']) {
+      const result = parse(`class${whitespace}Example {}/regex/.test('regex'); exports.value = 1`);
+      assert.deepStrictEqual(result.exports, ['value']);
+      assert.deepStrictEqual(result.reexports, []);
+    }
+    for (const source of [
+      'const className = {} / 2; exports.value = className',
+      'const close = {} / 2; exports.value = close',
+      'const value = {}; value.class = {} / 2; exports.value = value'
+    ]) {
+      const result = parse(source);
+      assert.deepStrictEqual(result.exports, ['value']);
+      assert.deepStrictEqual(result.reexports, []);
+    }
+  });
+
   test('Regexp division', () => {
     parse(`\nconst x = num / /'/.exec(l)[0].slice(1, -1)//'"`);
   });