fix(emulate-browsers): fix cross frame tostring

emulate-browsers/base/injected-scripts/_proxyUtils.ts

@@ -1,7 +1,7 @@
 /////// MASK TO STRING  ////////////////////////////////////////////////////////////////////////////////////////////////
 
 // eslint-disable-next-line prefer-const -- must be let: could change for different browser (ie, Safari)
-let nativeToStringFunctionString = Error.toString.toString();
+let nativeToStringFunctionString = `${Function.toString}`;
 // when functions are re-bound to work around the loss of scope issue in chromium, they blow up their native toString
 const overriddenFns = new Map<Function, string>();
 
@@ -11,9 +11,16 @@ Function.prototype.toString = new Proxy(Function.prototype.toString, {
     if (overriddenFns.has(thisArg)) {
       return overriddenFns.get(thisArg);
     }
-    if (target === Function.prototype.toString) {
-      return nativeToStringFunctionString;
+    // from puppeteer-stealth: Check if the toString prototype of the context is the same as the global prototype,
+    // if not indicates that we are doing a check across different windows
+    const hasSameProto = Object.getPrototypeOf(Function.prototype.toString).isPrototypeOf(
+      thisArg.toString,
+    );
+    if (hasSameProto === false) {
+      // Pass the call on to the local Function.prototype.toString instead
+      return thisArg.toString(...(args ?? []));
     }
+
     return target.apply(thisArg, args);
   },
 });

emulate-browsers/base/test/iframe.test.ts

@@ -26,6 +26,27 @@ test('should have a chrome object on iframes', async () => {
   expect(frameType).toBe('object');
 });
 
+test('should not break toString across frames', async () => {
+  const page = await createPage();
+
+  const toStrings = await page.evaluate(`(() => {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+
+  const contentWindow = iframe.contentWindow;
+  const fnCallWithFrame = contentWindow.Function.prototype.toString.call(Function.prototype.toString);
+  const fnToString = Function.toString + '';
+
+  return {
+    fnToString,
+    fnCallWithFrame
+  }
+})();`);
+
+  const { fnToString, fnCallWithFrame } = toStrings as any;
+  expect(fnToString).toBe(fnCallWithFrame);
+});
+
 test('should not break iframe functions', async () => {
   const page = await createPage();