RN: Implement `defineLazyObjectProperty`

Reviewed By: sahrens

Differential Revision: D3500318

fbshipit-source-id: 275c5b9a2b747174fb23b80896e2270eb2131e4b

Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js

@@ -91,37 +91,17 @@ function defineLazyProperty<T>(
   name: string,
   getNewValue: () => T
 ): void {
+  const defineLazyObjectProperty = require('defineLazyObjectProperty');
+
   const descriptor = getPropertyDescriptor(object, name);
   if (descriptor) {
     const backupName = `original${name[0].toUpperCase()}${name.substr(1)}`;
     Object.defineProperty(object, backupName, descriptor);
   }
-  const config = {
-    configurable: true,
+  defineLazyObjectProperty(object, name, {
+    get: getNewValue,
     enumerable: descriptor ? descriptor.enumerable !== false : true,
     writable: descriptor ? descriptor.writable !== false : true,
-  };
-  let value;
-  let valueSet = false;
-  function getValue(): T {
-    // WORKAROUND: A weird infinite loop occurs where calling `getValue` calls
-    // `setValue` which calls `Object.defineProperty` which somehow triggers
-    // `getValue` again. Adding `valueSet` breaks this loop.
-    if (!valueSet) {
-      setValue(getNewValue());
-    }
-    return value;
-  }
-  function setValue(newValue: T): void {
-    value = newValue;
-    valueSet = true;
-    Object.defineProperty(object, name, {...config, value: newValue});
-  }
-  Object.defineProperty(object, name, {
-    configurable: config.configurable,
-    enumerable: config.enumerable,
-    get: getValue,
-    set: setValue,
   });
 }
 

Libraries/Utilities/defineLazyObjectProperty.js

@@ -0,0 +1,61 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule defineLazyObjectProperty
+ * @flow
+ */
+
+'use strict';
+
+/**
+ * Defines a lazily evaluated property on the supplied `object`.
+ */
+function defineLazyObjectProperty<T>(
+  object: Object,
+  name: string,
+  descriptor: {
+    get: () => T,
+    enumerable?: boolean,
+    writable?: boolean,
+  },
+): void {
+  const {get} = descriptor;
+  const enumerable = descriptor.enumerable !== false;
+  const writable = descriptor.writable !== false;
+
+  let value;
+  let valueSet = false;
+  function getValue(): T {
+    // WORKAROUND: A weird infinite loop occurs where calling `getValue` calls
+    // `setValue` which calls `Object.defineProperty` which somehow triggers
+    // `getValue` again. Adding `valueSet` breaks this loop.
+    if (!valueSet) {
+      setValue(get());
+    }
+    return value;
+  }
+  function setValue(newValue: T): void {
+    value = newValue;
+    valueSet = true;
+    Object.defineProperty(object, name, {
+      value: newValue,
+      configurable: true,
+      enumerable,
+      writable,
+    });
+  }
+
+  Object.defineProperty(object, name, {
+    get: getValue,
+    set: setValue,
+    configurable: true,
+    enumerable,
+  });
+}
+
+module.exports = defineLazyObjectProperty;