Fix sessionStorage-related crash when running in sandboxed iframe (py…

…odide#5186)

Fixes this problem when Pyodide is running within a sandboxed iframe:

Uncaught SecurityError: Failed to read the 'sessionStorage' property from
'Window': The document is sandboxed and lacks the 'allow-same-origin' flag.

docs/project/changelog.md

@@ -66,6 +66,9 @@ myst:
 - {{ Fix }} JSPI support now works with support for new JSPI and no WebAssembly type reflection.
   {pr}`5129`
 
+- {{ Fix }} Fix sessionStorage-related crash when running in sandboxed iframe.
+  {pr}`5186`
+
 ### Packages
 
 - Upgraded `crc32c` to 2.7.1 {pr}`5169`

src/js/environments.ts

@@ -33,7 +33,7 @@ export const IN_BROWSER_MAIN_THREAD =
   typeof window === "object" &&
   typeof document === "object" &&
   typeof document.createElement === "function" &&
-  typeof sessionStorage === "object" &&
+  "sessionStorage" in window &&
   typeof importScripts !== "function";
 
 /** @private */