[Dev] Add support for manually rolling polyfills. Add polyfill for promise.withResolvers (#6103)

* Add polyfill for Promise.withResolvers

* Import polyfills in main

* Apply kev's suggestions from code review

Co-authored-by: NightKev <34855794+DayKev@users.noreply.github.com>

* Address comments from code review

---------

Co-authored-by: NightKev <34855794+DayKev@users.noreply.github.com>

src/main.ts

@@ -1,3 +1,6 @@
+import "#app/polyfills";
+// All polyfills MUST be loaded first for side effects
+
 import { InvertPostFX } from "#app/pipelines/invert";
 import { initI18n } from "#app/plugins/i18n";
 import { version } from "#package.json";

src/polyfills.ts

@@ -0,0 +1,21 @@
+/*
+Manual rolling of polyfills desired by the project.
+
+IMPORTANT: When adding / removing polyfills, ensure that typescript becomes
+aware of their existence, either by creating `src/typings/polyfills.d.ts`
+and defining them there, or or by adding the appropriate field polyfill to the
+`lib` property in `tsconfig.json`.
+*/
+
+if (typeof Promise.withResolvers === "undefined") {
+  Promise.withResolvers = <T>() => {
+    // Bangs are OK here; they are guaranteed to be defined when the promise is invoked.
+    let resolve!: (value: T | PromiseLike<T>) => void;
+    let reject!: (reason?: unknown) => void;
+    const promise = new Promise<T>((res, rej) => {
+      resolve = res;
+      reject = rej;
+    });
+    return { promise, resolve, reject };
+  };
+}

tsconfig.json

@@ -2,6 +2,17 @@
   "compilerOptions": {
     "target": "ES2020",
     "module": "ES2020",
+    // Modifying this option requires all values to be set manually because the defaults get overridden
+    // Values other than "ES2024.Promise" taken from https://github.com/microsoft/TypeScript/blob/main/src/lib/es2020.full.d.ts
+    "lib": [
+      "ES2020",
+      "ES2024.Promise",
+      "DOM",
+      "DOM.AsyncIterable",
+      "DOM.Iterable",
+      "ScriptHost",
+      "WebWorker.ImportScripts"
+    ],
     "moduleResolution": "bundler",
     "resolveJsonModule": true,
     "esModuleInterop": true,