Avoid reading the property if hasOwnProperty is false

Easy with an Object.assign polyfill

src/classic/element/ReactElementValidator.js

@@ -292,6 +292,19 @@ function warnForPropsMutation(propName, element) {
   );
 }
 
+// Inline Object.is polyfill
+function is(a, b) {
+  if (a !== a) {
+    // NaN
+    return b !== b;
+  }
+  if (a === 0 && b === 0) {
+    // +-0
+    return 1 / a === 1 / b;
+  }
+  return a === b;
+}
+
 /**
  * Given an element, check if its props have been mutated since element
  * creation (or the last call to this function). In particular, check if any
@@ -312,14 +325,8 @@ function checkAndWarnForMutatedProps(element) {
 
   for (var propName in props) {
     if (props.hasOwnProperty(propName)) {
-      var valueChanged = originalProps[propName] !== props[propName];
-      // Necessary because NaN !== NaN
-      if (typeof originalProps[propName] === 'number' &&
-          typeof props[propName] === 'number' &&
-          isNaN(originalProps[propName]) && isNaN(props[propName])) {
-        valueChanged = false;
-      }
-      if (!originalProps.hasOwnProperty(propName) || valueChanged) {
+      if (!originalProps.hasOwnProperty(propName) ||
+          !is(originalProps[propName], props[propName])) {
         warnForPropsMutation(propName, element);
 
         // Copy over the new value so that the two props objects match again

src/classic/element/__tests__/ReactElement-test.js

@@ -348,4 +348,17 @@ describe('ReactElement', function() {
       'Don\'t set .props.sound of the React component <Outer />.'
     );
   });
+
+  it('does not warn for NaN props', function() {
+    spyOn(console, 'warn');
+    var Test = React.createClass({
+      render: function() {
+        return <div />;
+      }
+    });
+    var test = ReactTestUtils.renderIntoDocument(<Test value={+undefined} />);
+    expect(test.props.value).toBeNaN();
+    expect(console.warn.argsForCall.length).toBe(0);
+  });
+
 });