Cache Platform constants in JS

Summary: For better perf with TurboModule, cache the return value of NativePlatformConstants*.getConstants() in JS so that we avoid going back into native (from JS) for each call. This specific method is called very frequently throughout RN codebase.

Reviewed By: mdvacca

Differential Revision: D15893289

fbshipit-source-id: ce8016ed7d3efb420df93e27dbfa77d7d4f06cf8

Libraries/Utilities/Platform.android.js

@@ -18,21 +18,25 @@ export type PlatformSelectSpec<A, D> = {
 };
 
 const Platform = {
+  __constants: null,
   OS: 'android',
   get Version() {
-    return NativePlatformConstantsAndroid.getConstants().Version;
+    return this.constants.Version;
   },
   get constants() {
-    return NativePlatformConstantsAndroid.getConstants();
+    if (this.__constants == null) {
+      this.__constants = NativePlatformConstantsAndroid.getConstants();
+    }
+    return this.__constants;
   },
   get isTesting(): boolean {
     if (__DEV__) {
-      return NativePlatformConstantsAndroid.getConstants().isTesting;
+      return this.constants.isTesting;
     }
     return false;
   },
   get isTV(): boolean {
-    return NativePlatformConstantsAndroid.getConstants().uiMode === 'tv';
+    return this.constants.uiMode === 'tv';
   },
   select: <A, D>(spec: PlatformSelectSpec<A, D>): A | D =>
     'android' in spec ? spec.android : spec.default,

Libraries/Utilities/Platform.ios.js

@@ -18,15 +18,19 @@ export type PlatformSelectSpec<D, I> = {
 };
 
 const Platform = {
+  __constants: null,
   OS: 'ios',
   get Version() {
-    return NativePlatformConstantsIOS.getConstants().osVersion;
+    return this.constants.osVersion;
   },
   get constants() {
-    return NativePlatformConstantsIOS.getConstants();
+    if (this.__constants == null) {
+      this.__constants = NativePlatformConstantsIOS.getConstants();
+    }
+    return this.__constants;
   },
   get isPad() {
-    return NativePlatformConstantsIOS.getConstants().interfaceIdiom === 'pad';
+    return this.constants.interfaceIdiom === 'pad';
   },
   /**
    * Deprecated, use `isTV` instead.
@@ -35,11 +39,11 @@ const Platform = {
     return Platform.isTV;
   },
   get isTV() {
-    return NativePlatformConstantsIOS.getConstants().interfaceIdiom === 'tv';
+    return this.constants.interfaceIdiom === 'tv';
   },
   get isTesting(): boolean {
     if (__DEV__) {
-      return NativePlatformConstantsIOS.getConstants().isTesting;
+      return this.constants.isTesting;
     }
     return false;
   },