From a89e9323fccf17ab3e5c3de9fcf22ec409baeef6 Mon Sep 17 00:00:00 2001
From: Kevin Gozali <fkg@fb.com>
Date: Tue, 18 Jun 2019 23:07:20 -0700
Subject: [PATCH] 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 | 12 ++++++++----
 Libraries/Utilities/Platform.ios.js     | 14 +++++++++-----
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/Libraries/Utilities/Platform.android.js b/Libraries/Utilities/Platform.android.js
index d7e672b33b8..e228adc98d2 100644
--- a/Libraries/Utilities/Platform.android.js
+++ b/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,
diff --git a/Libraries/Utilities/Platform.ios.js b/Libraries/Utilities/Platform.ios.js
index f558755c6f0..0bdb6d35a62 100644
--- a/Libraries/Utilities/Platform.ios.js
+++ b/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;
   },