Separate Object.is polyfill

packages/react-reconciler/src/ReactFiberNewContext.js

@@ -26,6 +26,7 @@ import {ContextProvider, ClassComponent} from 'shared/ReactWorkTags';
 
 import invariant from 'shared/invariant';
 import warning from 'shared/warning';
+import is from 'shared/objectIs';
 import {
   createUpdate,
   enqueueUpdate,
@@ -104,14 +105,7 @@ export function calculateChangedBits<T>(
   newValue: T,
   oldValue: T,
 ) {
-  // Use Object.is to compare the new context value to the old value. Inlined
-  // Object.is polyfill.
-  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
-  if (
-    (oldValue === newValue &&
-      (oldValue !== 0 || 1 / oldValue === 1 / (newValue: any))) ||
-    (oldValue !== oldValue && newValue !== newValue) // eslint-disable-line no-self-compare
-  ) {
+  if (is(oldValue, newValue)) {
     // No change
     return 0;
   } else {

packages/shared/areHookInputsEqual.js

@@ -8,6 +8,7 @@
  */
 
 import warning from 'shared/warning';
+import is from './objectIs';
 
 export default function areHookInputsEqual(arr1: any[], arr2: any[]) {
   // Don't bother comparing lengths in prod because these arrays should be
@@ -24,14 +25,7 @@ export default function areHookInputsEqual(arr1: any[], arr2: any[]) {
     );
   }
   for (let i = 0; i < arr1.length; i++) {
-    // Inlined Object.is polyfill.
-    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
-    const val1 = arr1[i];
-    const val2 = arr2[i];
-    if (
-      (val1 === val2 && (val1 !== 0 || 1 / val1 === 1 / (val2: any))) ||
-      (val1 !== val1 && val2 !== val2) // eslint-disable-line no-self-compare
-    ) {
+    if (is(arr1[i], arr2[i])) {
       continue;
     }
     return false;

packages/shared/objectIs.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+/**
+ * inlined Object.is polyfill to avoid requiring consumers ship their own
+ * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
+ */
+function is(x: any, y: any) {
+  return (
+    (x === y && (x !== 0 || 1 / x === 1 / y)) || (x !== x && y !== y) // eslint-disable-line no-self-compare
+  );
+}
+
+export default is;

packages/shared/shallowEqual.js

@@ -7,27 +7,10 @@
  * @flow
  */
 
-/*eslint-disable no-self-compare */
+import is from './objectIs';
 
 const hasOwnProperty = Object.prototype.hasOwnProperty;
 
-/**
- * inlined Object.is polyfill to avoid requiring consumers ship their own
- * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
- */
-function is(x, y) {
-  // SameValue algorithm
-  if (x === y) {
-    // Steps 1-5, 7-10
-    // Steps 6.b-6.e: +0 != -0
-    // Added the nonzero y check to make Flow happy, but it is redundant
-    return x !== 0 || y !== 0 || 1 / x === 1 / y;
-  } else {
-    // Step 6.a: NaN == NaN
-    return x !== x && y !== y;
-  }
-}
-
 /**
  * Performs equality by iterating through keys on an object and returning false
  * when any key has values which are not strictly equal between the arguments.