Create isolated globals (#554)

* Change to throw away iframe for capturing globals

* Fix iterators

Author: jonathanKingston

src/captured-globals.js

@@ -1,16 +1,50 @@
+/* global mozProxies */
+import { getInjectionElement } from './utils.js'
+export const hasMozProxies = typeof mozProxies !== 'undefined' ? mozProxies : false
+
+let dummyWindow
+if ('document' in globalThis &&
+    // Prevent infinate recursion of injection into Chrome
+    globalThis.location.href !== 'about:blank') {
+    const injectionElement = getInjectionElement()
+    // injectionElement is null in some playwright context tests
+    if (injectionElement) {
+        dummyWindow = document.createElement('iframe')
+        dummyWindow.style.display = 'none'
+        injectionElement.appendChild(dummyWindow)
+    }
+}
+
+let dummyContentWindow = dummyWindow?.contentWindow
+if (hasMozProxies) {
+    // @ts-expect-error - mozProxies is not defined on window
+    dummyContentWindow = dummyContentWindow.wrappedJSObject
+}
+// @ts-expect-error - Symbol is not defined on window
+const dummySymbol = dummyContentWindow?.Symbol
+const iteratorSymbol = dummySymbol?.iterator
+
 // Capture prototype to prevent overloading
-function captureGlobals (object) {
-    const newGlobal = object
-    for (const key in object) {
-        const value = object[key]
-        newGlobal[key] = value
+function captureGlobal (globalName) {
+    const global = dummyWindow?.contentWindow?.[globalName]
+
+    // if we were unable to create a dummy window, return the global
+    // this still has the advantage of preventing aliasing of the global through shawdowing
+    if (!global) {
+        return globalThis[globalName]
     }
-    for (const key in object.prototype) {
-        const value = object.prototype[key]
-        newGlobal.prototype[key] = value
+
+    // Alias the iterator symbol to the local symbol so for loops work
+    if (iteratorSymbol &&
+        global?.prototype &&
+        iteratorSymbol in global.prototype) {
+        global.prototype[Symbol.iterator] = global.prototype[iteratorSymbol]
     }
-    return newGlobal
+    return global
 }
 
-export const Set = captureGlobals(globalThis.Set)
-export const Reflect = captureGlobals(globalThis.Reflect)
+export const Set = captureGlobal('Set')
+export const Reflect = captureGlobal('Reflect')
+
+// Clean up the dummy window
+dummyWindow?.remove()