gaspaonrocks · July 26, 2018 14:14 · Jul 26, 2018
diff --git a/shallowEqual.js b/shallowEqual.js
@@ -0,0 +1,58 @@
+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;
+  }
+  // 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.
+ * Returns true when the values of all keys are strictly equal.
+ */
+function shallowEqual(objA, objB) {
+  if (is(objA, objB)) {
+    return true;
+  }
+
+  if (
+    typeof objA !== 'object' ||
+    objA === null ||
+    typeof objB !== 'object' ||
+    objB === null
+  ) {
+    return false;
+  }
+
+  const keysA = Object.keys(objA);
+  const keysB = Object.keys(objB);
+
+  if (keysA.length !== keysB.length) {
+    return false;
+  }
+
+  // Test for A's keys different from B.
+  for (let i = 0; i < keysA.length; i++) {
+    if (
+      !hasOwnProperty.call(objB, keysA[i]) ||
+      !is(objA[keysA[i]], objB[keysA[i]])
+    ) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+export default shallowEqual;
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