Exclude regenerator-runtime from production bundles

packages/react-native/Libraries/Core/setUpRegeneratorRuntime.js

@@ -18,29 +18,33 @@ const {polyfillGlobal} = require('../Utilities/PolyfillFunctions');
  * You can use this module directly, or just require InitializeCore.
  */
 
-let hasNativeGenerator;
-try {
-  // If this function was lowered by regenerator-transform, it will try to
-  // access `global.regeneratorRuntime` which doesn't exist yet and will throw.
-  hasNativeGenerator = hasNativeConstructor(
-    function* () {},
-    'GeneratorFunction',
-  );
-} catch {
-  // In this case, we know generators are not provided natively.
-  hasNativeGenerator = false;
-}
+// The preset only lowers generators in development builds, so the runtime is
+// only needed there. Gating on __DEV__ keeps it out of production bundles.
+if (__DEV__) {
+  let hasNativeGenerator;
+  try {
+    // If this function was lowered by regenerator-transform, it will try to
+    // access `global.regeneratorRuntime` which doesn't exist yet and will throw.
+    hasNativeGenerator = hasNativeConstructor(
+      function* () {},
+      'GeneratorFunction',
+    );
+  } catch {
+    // In this case, we know generators are not provided natively.
+    hasNativeGenerator = false;
+  }
 
-// If generators are provided natively, which suggests that there was no
-// regenerator-transform, then there is no need to set up the runtime.
-if (!hasNativeGenerator) {
-  polyfillGlobal('regeneratorRuntime', () => {
-    // The require just sets up the global, so make sure when we first
-    // invoke it the global does not exist
-    delete global.regeneratorRuntime;
+  // If generators are provided natively, which suggests that there was no
+  // regenerator-transform, then there is no need to set up the runtime.
+  if (!hasNativeGenerator) {
+    polyfillGlobal('regeneratorRuntime', () => {
+      // The require just sets up the global, so make sure when we first
+      // invoke it the global does not exist
+      delete global.regeneratorRuntime;
 
-    // regenerator-runtime/runtime exports the regeneratorRuntime object, so we
-    // can return it safely.
-    return require('regenerator-runtime/runtime'); // flowlint-line untyped-import:off
-  });
+      // regenerator-runtime/runtime exports the regeneratorRuntime object, so we
+      // can return it safely.
+      return require('regenerator-runtime/runtime'); // flowlint-line untyped-import:off
+    });
+  }
 }