Add init_scripts support to BrowserConfig for pre-page-load JS injection

This adds the ability to inject JavaScript that runs before any page loads,
useful for stealth evasions (canvas/audio fingerprinting, userAgentData).

- Add init_scripts parameter to BrowserConfig (list of JS strings)
- Apply init_scripts in setup_context() via context.add_init_script()
- Update from_kwargs() and to_dict() for serialization

crawl4ai/async_configs.py

@@ -477,6 +477,7 @@ class BrowserConfig:
         debugging_port: int = 9222,
         host: str = "localhost",
         enable_stealth: bool = False,
+        init_scripts: List[str] = None,
     ):
         
         self.browser_type = browser_type
@@ -536,6 +537,7 @@ class BrowserConfig:
         self.debugging_port = debugging_port
         self.host = host
         self.enable_stealth = enable_stealth
+        self.init_scripts = init_scripts if init_scripts is not None else []
 
         fa_user_agenr_generator = ValidUAGenerator()
         if self.user_agent_mode == "random":
@@ -615,6 +617,7 @@ class BrowserConfig:
             debugging_port=kwargs.get("debugging_port", 9222),
             host=kwargs.get("host", "localhost"),
             enable_stealth=kwargs.get("enable_stealth", False),
+            init_scripts=kwargs.get("init_scripts", []),
         )
 
     def to_dict(self):
@@ -654,9 +657,10 @@ class BrowserConfig:
             "debugging_port": self.debugging_port,
             "host": self.host,
             "enable_stealth": self.enable_stealth,
+            "init_scripts": self.init_scripts,
         }
 
-                
+
         return result
 
     def clone(self, **kwargs):

crawl4ai/browser_manager.py

@@ -890,7 +890,12 @@ class BrowserManager:
                 or crawlerRunConfig.simulate_user
                 or crawlerRunConfig.magic
             ):
-                await context.add_init_script(load_js_script("navigator_overrider"))        
+                await context.add_init_script(load_js_script("navigator_overrider"))
+
+        # Apply custom init_scripts from BrowserConfig (for stealth evasions, etc.)
+        if self.config.init_scripts:
+            for script in self.config.init_scripts:
+                await context.add_init_script(script)
 
     async def create_browser_context(self, crawlerRunConfig: CrawlerRunConfig = None):
         """