refactor(ses): commons async gen fn instance to avoid name dance

endojs · Sep 23, 2024 · 02271af · 02271af
1 parent 0bff9a0
commit 02271af
Showing 1 changed file with 29 additions and 27 deletions.
diff --git a/packages/ses/src/commons.js b/packages/ses/src/commons.js
@@ -379,31 +379,33 @@ export const FERAL_STACK_GETTER = feralStackGetter;
  */
 export const FERAL_STACK_SETTER = feralStackSetter;
 
-// Test for async generator function syntax support.
-let AsyncGeneratorNewFunctionInstance;
-try {
-  // Wrapping one in an new Function lets the `hermesc` binary file
-  // parse the Metro js bundle without SyntaxError, to generate the
-  // optimised Hermes bytecode bundle, when `gradlew` is called to
-  // assemble the release build APK for React Native prod Android apps.
-  // Delaying the error until runtime lets us customise lockdown behaviour.
-  AsyncGeneratorNewFunctionInstance = new FERAL_FUNCTION(
-    'return (async function* AsyncGeneratorFunctionInstance() {})',
-  )();
-} catch (e) {
-  // @ts-expect-error ts(2339) Property 'jsEngine' does not exist on type 'Error'. However it exists on Hermes.
-  if (Error.prototype.jsEngine === 'hermes' && e.name === 'SyntaxError') {
-    // Swallows Hermes error `async generators are unsupported` at runtime.
-    // @ts-expect-error ts(2554) Expected 0 arguments, but got 1. It refers to the Web API Window object, but on Hermes we expect 1 argument.
-    // eslint-disable-next-line no-undef
-    print('SES: Skipping async generators, unsupported on Hermes');
-    // Note: `console` is not a JS built-in, so Hermes engine throws:
-    // Uncaught ReferenceError: Property 'console' doesn't exist
-    // See: https://github.com/facebook/hermes/issues/675
-    // However React Native provides a `console` implementation:
-    // https://github.com/facebook/react-native/blob/main/packages/react-native/Libraries/Core/InitializeCore.js
-  } else {
-    throw e;
-  }
+// eslint-disable-next-line consistent-return
+const getAsyncGeneratorFunctionInstance = () => {
+  // Test for async generator function syntax support.
+  try {
+    // Wrapping one in an new Function lets the `hermesc` binary file
+    // parse the Metro js bundle without SyntaxError, to generate the
+    // optimised Hermes bytecode bundle, when `gradlew` is called to
+    // assemble the release build APK for React Native prod Android apps.
+    // Delaying the error until runtime lets us customise lockdown behaviour.
+    return new FERAL_FUNCTION(
+      'return (async function* AsyncGeneratorFunctionInstance() {})',
+    )();
+  } catch (e) {
+    // @ts-expect-error ts(2339) Property 'jsEngine' does not exist on type 'Error'. However it exists on Hermes.
+    if (Error.prototype.jsEngine === 'hermes' && e.name === 'SyntaxError') {
+      // Swallows Hermes error `async generators are unsupported` at runtime.
+      // @ts-expect-error ts(2554) Expected 0 arguments, but got 1. It refers to the Web API Window object, but on Hermes we expect 1 argument.
+      // eslint-disable-next-line no-undef
+      print('SES: Skipping async generators, unsupported on Hermes');
+      // Note: `console` is not a JS built-in, so Hermes engine throws:
+      // Uncaught ReferenceError: Property 'console' doesn't exist
+      // See: https://github.com/facebook/hermes/issues/675
+      // However React Native provides a `console` implementation:
+      // https://github.com/facebook/react-native/blob/main/packages/react-native/Libraries/Core/InitializeCore.js
+    } else {
+      throw e;
+    }
+}
 }
-export const AsyncGeneratorFunctionInstance = AsyncGeneratorNewFunctionInstance;
+export const AsyncGeneratorFunctionInstance = getAsyncGeneratorFunctionInstance();