Unbreak refs

If no refs are rendered, `this.refs` is undefined. This is bad since it deopts & is hard to look for. Instead we should make `this.refs` an immutable empty object.

src/core/ReactCompositeComponent.js

@@ -767,6 +767,7 @@ var ReactCompositeComponentMixin = {
   construct: function(initialProps, children) {
     // Children can be either an array or more than one argument
     ReactComponent.Mixin.construct.apply(this, arguments);
+    ReactOwner.Mixin.construct.apply(this, arguments);
 
     this.state = null;
     this._pendingState = null;
@@ -873,10 +874,7 @@ var ReactCompositeComponentMixin = {
     this._renderedComponent = null;
 
     ReactComponent.Mixin.unmountComponent.call(this);
-
-    if (this.refs) {
-      this.refs = null;
-    }
+    ReactOwner.Mixin.unmountComponent.call(this);
 
     // Some existing components rely on this.props even after they've been
     // destroyed (in event handlers).

src/core/ReactOwner.js

@@ -18,6 +18,7 @@
 
 "use strict";
 
+var emptyObject = require('emptyObject');
 var invariant = require('invariant');
 
 /**
@@ -118,6 +119,10 @@ var ReactOwner = {
    */
   Mixin: {
 
+    construct: function() {
+      this.refs = emptyObject;
+    },
+
     /**
      * Lazily allocates the refs object and stores `component` as `ref`.
      *
@@ -132,7 +137,7 @@ var ReactOwner = {
         'attachRef(%s, ...): Only a component\'s owner can store a ref to it.',
         ref
       );
-      var refs = this.refs || (this.refs = {});
+      var refs = this.refs === emptyObject ? (this.refs = {}) : this.refs;
       refs[ref] = component;
     },
 
@@ -145,6 +150,10 @@ var ReactOwner = {
      */
     detachRef: function(ref) {
       delete this.refs[ref];
+    },
+
+    unmountComponent: function() {
+      this.refs = null;
     }
 
   }

src/core/__tests__/refs-test.js

@@ -236,5 +236,17 @@ describe('ref swapping', function() {
     expect(refHopsAround.refs.divTwoRef).toEqual(secondDiv);
     expect(refHopsAround.refs.divThreeRef).toEqual(thirdDiv);
   });
+
+
+  it('always has a value for this.refs', function() {
+    var Component = React.createClass({
+      render: function() {
+        return <div />;
+      }
+    });
+
+    var instance = ReactTestUtils.renderIntoDocument(<Component />);
+    expect(!!instance.refs).toBe(true);
+  });
 });
 

src/utils/__tests__/cloneWithProps-test.js

@@ -24,6 +24,7 @@ require('mock-modules').dontMock('cloneWithProps');
 var mocks = require('mocks');
 
 var cloneWithProps = require('cloneWithProps');
+var emptyObject = require('emptyObject');
 
 var React;
 var ReactTestUtils;
@@ -107,7 +108,7 @@ describe('cloneWithProps', function() {
       console.warn = mocks.getMockFunction();
 
       var component = ReactTestUtils.renderIntoDocument(<Grandparent />);
-      expect(component.refs).toBe(undefined);
+      expect(component.refs).toBe(emptyObject);
       expect(console.warn.mock.calls.length).toBe(1);
     } finally {
       console.warn = _warn;