From 1db95907e6dbfed553666add26dce9d72a47ff97 Mon Sep 17 00:00:00 2001
From: huliang <498755303@qq.com>
Date: Wed, 22 Jul 2026 22:42:05 +0800
Subject: [PATCH] fix: cache isFireFox() result in CSSParser to avoid repeated
 UA scan

recordResult() runs once per CSS fragment and called isFireFox() every
time, so a single stylesheet triggers thousands of avoidable UA substring
scans. Cache the result into this.isFF once at the start of exec(), reuse
it in recordResult() and the return value, and reset it in reset().
---
 src/sandbox/scoped_css.ts | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/sandbox/scoped_css.ts b/src/sandbox/scoped_css.ts
index 1fadfa33..f8bed36e 100644
--- a/src/sandbox/scoped_css.ts
+++ b/src/sandbox/scoped_css.ts
@@ -35,6 +35,7 @@ class CSSParser {
   private scopecssDisableSelectors: Array<string> = [] // disable or enable scopecss for specific selectors
   private scopecssDisableNextLine = false // use block comments /* scopecss-disable-next-line */ to disable scopecss on a specific line
   private optionCssSelectors: Array<string> = [] // use this option to include specific selectors, so that they will be affected by scopecss ,like microApp.options.optionCss
+  private isFF = false // cache isFireFox() result per exec, avoid repeated UA scan in recordResult
 
   public exec (
     cssText: string,
@@ -46,11 +47,13 @@ class CSSParser {
     this.prefix = prefix
     this.baseURI = baseURI
     this.linkPath = linkPath || ''
+    // cache isFireFox() once per exec, recordResult runs for every fragment
+    this.isFF = isFireFox()
     // fetch optionCss configure
     this.optionCssSelectors = microApp.options.optionCss || []
 
     this.matchRules()
-    return isFireFox() ? decodeURIComponent(this.result) : this.result
+    return this.isFF ? decodeURIComponent(this.result) : this.result
   }
 
   public reset (): void {
@@ -58,6 +61,7 @@ class CSSParser {
     this.scopecssDisable = this.scopecssDisableNextLine = false
     this.scopecssDisableSelectors = []
     this.optionCssSelectors = []
+    this.isFF = false
   }
 
   // core action for match rules
@@ -471,7 +475,7 @@ class CSSParser {
   // splice string
   private recordResult (strFragment: string): void {
     // Firefox performance degradation when string contain special characters, see https://github.com/jd-opensource/micro-app/issues/256
-    if (isFireFox()) {
+    if (this.isFF) {
       this.result += encodeURIComponent(strFragment)
     } else {
       this.result += strFragment