diff --git a/posthog/api/site_app.py b/posthog/api/site_app.py
index 6704ff0c7f534..1d692b943a084 100644
--- a/posthog/api/site_app.py
+++ b/posthog/api/site_app.py
@@ -7,6 +7,9 @@
 from statshog.defaults.django import statsd
 
 from posthog.exceptions import generate_exception_response
+from posthog.hogql import ast
+from posthog.hogql.compiler.javascript import JavaScriptCompiler
+from posthog.hogql.parser import parse_string_template
 from posthog.logging.timing import timed
 from posthog.plugins.site import get_site_config_from_schema, get_transpiled_site_source
 
@@ -22,7 +25,48 @@ def get_site_app(request: HttpRequest, id: int, token: str, hash: str) -> HttpRe
         id = source_file.id
         source = source_file.source
         config = get_site_config_from_schema(source_file.config_schema, source_file.config)
-        response = f"{source}().inject({{config:{json.dumps(config)},posthog:window['__$$ph_site_app_{id}']}})"
+
+        # Wrap in IIFE = Immediately Invoked Function Expression = to avoid polluting global scope
+        response = "(function() {\n\n"
+
+        # Build a switch statement within a try/catch loop and a static dict
+        config_switch = ""
+        config_dict_items: list[str] = []
+
+        compiler = JavaScriptCompiler()
+        for key, value in config.items():
+            key_string = json.dumps(str(key) or "<empty>")
+            if isinstance(value, str) and "{" in value:
+                base_code = compiler.visit(ast.ReturnStatement(expr=parse_string_template(value)))
+                config_switch += f"case {key_string}: {base_code};\n"
+                config_dict_items.append(f"{key_string}: getConfigKey({json.dumps(key)}, initial)")
+            else:
+                config_dict_items.append(f"{key_string}: {json.dumps(value)}")
+
+        # Start with the STL functions
+        response += compiler.get_inlined_stl() + "\n"
+
+        # This will be used by Hog code to access globals
+        response += "let __globals = {};\n"
+        response += "function __getGlobal(key) { return __globals[key] }\n"
+
+        if config_switch:
+            response += (
+                f"function getConfigKey(key, initial) {{ try {{ switch (key) {{\n\n///// calculated properties\n"
+            )
+            response += config_switch
+            response += "\ndefault: return null; }\n"
+            response += "} catch (e) { if(!initial) {console.warn('[POSTHOG-JS] Unable to get config field', key, e);} return null } }\n"
+
+        response += (
+            f"function getConfig(globals, initial) {{ __globals = globals || {'{}'}; return {{\n\n///// config\n"
+        )
+        response += ",\n".join(config_dict_items)
+        response += "\n\n} }\n"
+
+        response += f"{source}().inject({{config:getConfig({'{}'}, true),getConfig:getConfig,posthog:window['__$$ph_site_app_{id}']}});"
+
+        response += "\n\n})();"
 
         statsd.incr(f"posthog_cloud_raw_endpoint_success", tags={"endpoint": "site_app"})
         return HttpResponse(content=response, content_type="application/javascript")
diff --git a/posthog/hogql/compiler/javascript.py b/posthog/hogql/compiler/javascript.py
index b5c46b3ba1955..14d405c2e6777 100644
--- a/posthog/hogql/compiler/javascript.py
+++ b/posthog/hogql/compiler/javascript.py
@@ -12,7 +12,7 @@
 from posthog.hogql.visitor import Visitor
 
 # TODO: make sure _JS_GET_GLOBAL is unique!
-_JS_GET_GLOBAL = "get_global"
+_JS_GET_GLOBAL = "__getGlobal"
 _JS_KEYWORDS = ["var", "let", "const", "function", "typeof", "Error"]
 
 
@@ -52,7 +52,7 @@ def create_javascript(
     supported_functions = supported_functions or set()
     compiler = JavaScriptCompiler(supported_functions, args, context, in_repl, locals)
     base_code = compiler.visit(expr)
-    import_code = import_stl_functions(compiler.inlined_stl)
+    import_code = compiler.get_inlined_stl()
     code = import_code + ("\n\n" if import_code else "") + base_code
     return CompiledJavaScript(code=code, locals=compiler.locals)
 
@@ -95,6 +95,9 @@ def __init__(
         for arg in self.args:
             self._declare_local(arg)
 
+    def get_inlined_stl(self) -> str:
+        return import_stl_functions(self.inlined_stl)
+
     def _start_scope(self):
         self.scope_depth += 1