From 2e095b4140724b11118f2ed458a34e3d8ceddfad Mon Sep 17 00:00:00 2001
From: Brian Vaughn <brian.david.vaughn@gmail.com>
Date: Thu, 9 Feb 2017 14:10:45 -1000
Subject: [PATCH] Hardened validateCallback to better handle null values
 (#8973)

Previously, calls to validateCallback() with a null callback value resulted in runtime errors if a certain transform was not applied prior to running. This commit wraps the invariant() with the condition check so as to avoid calling formatUnexpectedArgument() unless necessary. It also replaces the truthy/falsy callback check with an explicit check for improved performance.
---
 .../shared/utils/validateCallback.js          | 20 ++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/src/renderers/shared/utils/validateCallback.js b/src/renderers/shared/utils/validateCallback.js
index 64da06082c..65c0260db9 100644
--- a/src/renderers/shared/utils/validateCallback.js
+++ b/src/renderers/shared/utils/validateCallback.js
@@ -28,13 +28,19 @@ function formatUnexpectedArgument(arg: any) {
 }
 
 function validateCallback(callback: ?Function, callerName: string) {
-  invariant(
-    !callback || typeof callback === 'function',
-    '%s(...): Expected the last optional `callback` argument to be a ' +
-    'function. Instead received: %s.',
-    callerName,
-    formatUnexpectedArgument(callback)
-  );
+  if (
+    callback !== null &&
+    callback !== undefined &&
+    typeof callback !== 'function'
+  ) {
+    invariant(
+      false,
+      '%s(...): Expected the last optional `callback` argument to be a ' +
+      'function. Instead received: %s.',
+      callerName,
+      formatUnexpectedArgument(callback)
+    );
+  }
 }
 
 module.exports = validateCallback;