Back out "ESM plugin bundles"

Summary:
Original commit changeset: 2a60315dd5c0

Original Phabricator Diff: D50015827

Reviewed By: lblasa

Differential Revision: D50168201

fbshipit-source-id: 3430c37b0aa6a5e3a5ec35fb4c54f01899236173

desktop/flipper-ui-browser/src/initializeRenderHost.tsx

@@ -177,19 +177,25 @@ export function initializeRenderHost(
     },
     flipperServer,
     async requirePlugin(path): Promise<{plugin: any; css?: string}> {
-      /** path to bundle.js from project root */
-      const staticPath = path.includes('/static/')
-        ? path.split('/static/', 2).pop()
-        : path.split('/desktop/', 2).pop();
-      // This is a string as server side is transpiled by typescript.
-      // Typescript transpiles dynamic import calls to `require` in the browser bundle
-      // We want to explicilty use dynamic import here
-      const importStr = `import('/${staticPath}?ts=${Date.now()}')`;
       const source = await flipperServer.exec('plugin-source', path);
-      // eslint-disable-next-line no-eval
-      const importRes = await eval(importStr);
 
-      return {plugin: importRes, css: source.css};
+      let js = source.js;
+      // append source url (to make sure a file entry shows up in the debugger)
+      js += `\n//# sourceURL=file://${path}`;
+      if (isProduction()) {
+        // and source map url (to get source code if available)
+        js += `\n//# sourceMappingURL=file://${path}.map`;
+      }
+
+      // Plugins are compiled as typical CJS modules, referring to the global
+      // 'module', which we'll make available by loading the source into a closure that captures 'module'.
+      // Note that we use 'eval', and not 'new Function', because the latter will cause the source maps
+      // to be off by two lines (as the function declaration uses two lines in the generated source)
+      // eslint-disable-next-line no-eval
+      const cjsLoader = eval('(module) => {' + js + '\n}');
+      const theModule = {exports: {}};
+      cjsLoader(theModule);
+      return {plugin: theModule.exports, css: source.css};
     },
     getStaticResourceUrl(path): string {
       // the 'static' folder is mounted as static middleware in Express at the root