From 3ae9ad57fcae7c5767f8dd93a96d393b30807047 Mon Sep 17 00:00:00 2001
From: Toad06 <gd.productions@laposte.net>
Date: Wed, 30 Dec 2020 20:41:34 +0100
Subject: [PATCH] web: Prevent crashes when native `Window` is overridden

---
 web/packages/core/src/js-polyfills.ts | 58 ++++++++++++++++++++++++++-
 web/packages/core/src/load-ruffle.ts  | 13 ++----
 2 files changed, 61 insertions(+), 10 deletions(-)

diff --git a/web/packages/core/src/js-polyfills.ts b/web/packages/core/src/js-polyfills.ts
index 323f0ddfb..48e805e05 100644
--- a/web/packages/core/src/js-polyfills.ts
+++ b/web/packages/core/src/js-polyfills.ts
@@ -1,4 +1,5 @@
 /* eslint @typescript-eslint/no-explicit-any: "off" */
+/* eslint @typescript-eslint/ban-types: "off" */
 
 declare global {
     interface Window {
@@ -14,7 +15,7 @@ declare global {
  * https://tc39.github.io/ecma262/#sec-array.prototype.reduce
  *
  */
-export function setArrayPrototypeReduce(): any {
+function polyfillArrayPrototypeReduce(): any {
     Object.defineProperty(Array.prototype, "reduce", {
         value: function (...args: any) {
             if (
@@ -67,3 +68,58 @@ export function setArrayPrototypeReduce(): any {
         },
     });
 }
+
+/**
+ * Polyfills the `Window` function.
+ *
+ */
+function polyfillWindow(): void {
+    if (
+        typeof window.constructor !== "function" ||
+        !isNativeFunction(window.constructor)
+    ) {
+        // Don't polyfill `Window` if `window.constructor` has been overridden.
+        return;
+    }
+    // @ts-expect-error: `Function not assignable to { new (): Window; prototype: Window; }`
+    window.Window = window.constructor;
+}
+
+/**
+ * Determines whether a function is native or not.
+ *
+ * @param func The function to test.
+ * @returns True if the function hasn't been overridden.
+ */
+function isNativeFunction(func: Function): boolean {
+    const val =
+        typeof Function.prototype.toString === "function"
+            ? Function.prototype.toString()
+            : null;
+    if (typeof val === "string" && val.indexOf("[native code]") >= 0) {
+        return (
+            Function.prototype.toString.call(func).indexOf("[native code]") >= 0
+        );
+    }
+    return false;
+}
+
+/**
+ * Checks and applies the polyfills to the current window, if needed.
+ *
+ */
+export function setPolyfillsOnLoad(): void {
+    if (
+        typeof Array.prototype.reduce !== "function" ||
+        !isNativeFunction(Array.prototype.reduce)
+    ) {
+        // Some external libraries override the `Array.prototype.reduce` method in a way
+        // that causes Webpack to crash (#1507, #1865), so we need to override it again.
+        polyfillArrayPrototypeReduce();
+    }
+    if (typeof Window !== "function" || !isNativeFunction(Window)) {
+        // Overriding the native `Window` function causes issues in wasm-bindgen, as a
+        // code like `window instanceof Window` will no longer work.
+        polyfillWindow();
+    }
+}
diff --git a/web/packages/core/src/load-ruffle.ts b/web/packages/core/src/load-ruffle.ts
index c37461a3d..0ff4eccb8 100644
--- a/web/packages/core/src/load-ruffle.ts
+++ b/web/packages/core/src/load-ruffle.ts
@@ -6,7 +6,7 @@
 
 import { Ruffle } from "../pkg/ruffle_web";
 
-import { setArrayPrototypeReduce } from "./js-polyfills";
+import { setPolyfillsOnLoad } from "./js-polyfills";
 
 /**
  * Load ruffle from an automatically-detected location.
@@ -19,14 +19,9 @@ import { setArrayPrototypeReduce } from "./js-polyfills";
  * instances.
  */
 async function fetchRuffle(): Promise<{ new (...args: any[]): Ruffle }> {
-    if (
-        typeof Array.prototype.reduce !== "function" ||
-        Array.prototype.reduce.toString().indexOf("[native code]") === -1
-    ) {
-        // Some external libraries override the `Array.prototype.reduce` method in a way
-        // that causes Webpack to crash (#1507, #1865), so we need to override it again.
-        setArrayPrototypeReduce();
-    }
+    // Apply some pure JavaScript polyfills to prevent conflicts with external
+    // libraries, if needed.
+    setPolyfillsOnLoad();
 
     try {
         // If ruffleRuntimePath is defined then we are executing inside the extension