Adds createRef() as per RFC

packages/react-dom/src/__tests__/ReactComponent-test.js

@@ -162,7 +162,7 @@ describe('ReactComponent', () => {
     ReactTestUtils.renderIntoDocument(<Parent child={<span />} />);
   });
 
-  it('should support new-style refs', () => {
+  it('should support callback-style refs', () => {
     const innerObj = {};
     const outerObj = {};
 
@@ -202,6 +202,49 @@ describe('ReactComponent', () => {
     expect(mounted).toBe(true);
   });
 
+  it('should support object-style refs', () => {
+    const innerObj = {};
+    const outerObj = {};
+
+    class Wrapper extends React.Component {
+      getObject = () => {
+        return this.props.object;
+      };
+
+      render() {
+        return <div>{this.props.children}</div>;
+      }
+    }
+
+    let mounted = false;
+
+    class Component extends React.Component {
+      constructor() {
+        super();
+        this.innerRef = React.createRef();
+        this.outerRef = React.createRef();
+      }
+      render() {
+        const inner = <Wrapper object={innerObj} ref={this.innerRef} />;
+        const outer = (
+          <Wrapper object={outerObj} ref={this.outerRef}>
+            {inner}
+          </Wrapper>
+        );
+        return outer;
+      }
+
+      componentDidMount() {
+        expect(this.innerRef.value.getObject()).toEqual(innerObj);
+        expect(this.outerRef.value.getObject()).toEqual(outerObj);
+        mounted = true;
+      }
+    }
+
+    ReactTestUtils.renderIntoDocument(<Component />);
+    expect(mounted).toBe(true);
+  });
+
   it('should support new-style refs with mixed-up owners', () => {
     class Wrapper extends React.Component {
       getTitle = () => {

packages/react-dom/src/__tests__/ReactErrorBoundaries-test.js

@@ -937,7 +937,7 @@ describe('ReactErrorBoundaries', () => {
     expect(log).toEqual(['ErrorBoundary componentWillUnmount']);
   });
 
-  it('resets refs if mounting aborts', () => {
+  it('resets callback refs if mounting aborts', () => {
     function childRef(x) {
       log.push('Child ref is set to ' + x);
     }
@@ -981,6 +981,44 @@ describe('ReactErrorBoundaries', () => {
     ]);
   });
 
+  it('resets object refs if mounting aborts', () => {
+    let childRef = React.createRef();
+    let errorMessageRef = React.createRef();
+
+    const container = document.createElement('div');
+    ReactDOM.render(
+      <ErrorBoundary errorMessageRef={errorMessageRef}>
+        <div ref={childRef} />
+        <BrokenRender />
+      </ErrorBoundary>,
+      container,
+    );
+    expect(container.textContent).toBe('Caught an error: Hello.');
+    expect(log).toEqual([
+      'ErrorBoundary constructor',
+      'ErrorBoundary componentWillMount',
+      'ErrorBoundary render success',
+      'BrokenRender constructor',
+      'BrokenRender componentWillMount',
+      'BrokenRender render [!]',
+      // Handle error:
+      // Finish mounting with null children
+      'ErrorBoundary componentDidMount',
+      // Handle the error
+      'ErrorBoundary componentDidCatch',
+      // Render the error message
+      'ErrorBoundary componentWillUpdate',
+      'ErrorBoundary render error',
+      'ErrorBoundary componentDidUpdate',
+    ]);
+    expect(errorMessageRef.value.toString()).toEqual('[object HTMLDivElement]');
+
+    log.length = 0;
+    ReactDOM.unmountComponentAtNode(container);
+    expect(log).toEqual(['ErrorBoundary componentWillUnmount']);
+    expect(errorMessageRef.value).toEqual(null);
+  });
+
   it('successfully mounts if no error occurs', () => {
     const container = document.createElement('div');
     ReactDOM.render(

packages/react-reconciler/src/ReactChildFiber.js

@@ -104,7 +104,11 @@ function coerceRef(
   element: ReactElement,
 ) {
   let mixedRef = element.ref;
-  if (mixedRef !== null && typeof mixedRef !== 'function') {
+  if (
+    mixedRef !== null &&
+    typeof mixedRef !== 'function' &&
+    typeof mixedRef !== 'object'
+  ) {
     if (__DEV__) {
       if (returnFiber.mode & StrictMode) {
         const componentName = getComponentName(returnFiber) || 'Component';
@@ -113,7 +117,7 @@ function coerceRef(
             false,
             'A string ref has been found within a strict mode tree. ' +
               'String refs are a source of potential bugs and should be avoided. ' +
-              'We recommend using a ref callback instead.' +
+              'We recommend using createRef() instead.' +
               '\n%s' +
               '\n\nLearn more about using refs safely here:' +
               '\nhttps://fb.me/react-strict-mode-string-ref',

packages/react-reconciler/src/ReactFiber.js

@@ -7,7 +7,7 @@
  */
 
 import type {ReactElement, Source} from 'shared/ReactElementType';
-import type {ReactPortal} from 'shared/ReactTypes';
+import type {ReactPortal, RefObject} from 'shared/ReactTypes';
 import type {TypeOfWork} from 'shared/ReactTypeOfWork';
 import type {TypeOfMode} from './ReactTypeOfMode';
 import type {TypeOfSideEffect} from 'shared/ReactTypeOfSideEffect';
@@ -107,7 +107,7 @@ export type Fiber = {|
 
   // The ref last used to attach this node.
   // I'll avoid adding an owner field for prod and model that as functions.
-  ref: null | (((handle: mixed) => void) & {_stringRef: ?string}),
+  ref: null | (((handle: mixed) => void) & {_stringRef: ?string}) | RefObject,
 
   // Input is the data coming into process this fiber. Arguments. Props.
   pendingProps: any, // This type will be more specific once we overload the tag.

packages/react-reconciler/src/ReactFiberCommitWork.js

@@ -77,18 +77,22 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
   function safelyDetachRef(current: Fiber) {
     const ref = current.ref;
     if (ref !== null) {
-      if (__DEV__) {
-        invokeGuardedCallback(null, ref, null, null);
-        if (hasCaughtError()) {
-          const refError = clearCaughtError();
-          captureError(current, refError);
+      if (typeof ref === 'function') {
+        if (__DEV__) {
+          invokeGuardedCallback(null, ref, null, null);
+          if (hasCaughtError()) {
+            const refError = clearCaughtError();
+            captureError(current, refError);
+          }
+        } else {
+          try {
+            ref(null);
+          } catch (refError) {
+            captureError(current, refError);
+          }
         }
       } else {
-        try {
-          ref(null);
-        } catch (refError) {
-          captureError(current, refError);
-        }
+        ref.value = null;
       }
     }
   }
@@ -175,20 +179,30 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
     const ref = finishedWork.ref;
     if (ref !== null) {
       const instance = finishedWork.stateNode;
+      let instanceToUse;
       switch (finishedWork.tag) {
         case HostComponent:
-          ref(getPublicInstance(instance));
+          instanceToUse = getPublicInstance(instance);
           break;
         default:
-          ref(instance);
+          instanceToUse = instance;
+      }
+      if (typeof ref === 'function') {
+        ref(instanceToUse);
+      } else {
+        ref.value = instanceToUse;
       }
     }
   }
 
   function commitDetachRef(current: Fiber) {
     const currentRef = current.ref;
     if (currentRef !== null) {
-      currentRef(null);
+      if (typeof currentRef === 'function') {
+        currentRef(null);
+      } else {
+        currentRef.value = null;
+      }
     }
   }
 

packages/react/src/React.js

@@ -14,6 +14,7 @@ import {
 } from 'shared/ReactSymbols';
 
 import {Component, PureComponent} from './ReactBaseClasses';
+import {createRef} from './ReactCreateRef';
 import {forEach, map, count, toArray, only} from './ReactChildren';
 import ReactCurrentOwner from './ReactCurrentOwner';
 import {
@@ -39,6 +40,7 @@ const React = {
     only,
   },
 
+  createRef,
   Component,
   PureComponent,
 

packages/react/src/ReactCreateRef.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @flow
+ */
+
+import type {RefObject} from 'shared/ReactTypes';
+
+// an immutable object with a single mutable value
+export function createRef(): RefObject {
+  const refObject = {
+    value: null,
+  };
+  if (__DEV__) {
+    Object.seal(refObject);
+  }
+  return refObject;
+}

packages/react/src/__tests__/ReactStrictMode-test.internal.js

@@ -778,7 +778,7 @@ describe('ReactStrictMode', () => {
       }).toWarnDev(
         'Warning: A string ref has been found within a strict mode tree. ' +
           'String refs are a source of potential bugs and should be avoided. ' +
-          'We recommend using a ref callback instead.\n\n' +
+          'We recommend using createRef() instead.\n\n' +
           '    in OuterComponent (at **)\n\n' +
           'Learn more about using refs safely here:\n' +
           'https://fb.me/react-strict-mode-string-ref',
@@ -819,7 +819,7 @@ describe('ReactStrictMode', () => {
       }).toWarnDev(
         'Warning: A string ref has been found within a strict mode tree. ' +
           'String refs are a source of potential bugs and should be avoided. ' +
-          'We recommend using a ref callback instead.\n\n' +
+          'We recommend using createRef() instead.\n\n' +
           '    in InnerComponent (at **)\n' +
           '    in OuterComponent (at **)\n\n' +
           'Learn more about using refs safely here:\n' +

packages/shared/ReactTypes.js

@@ -97,3 +97,7 @@ export type ReactPortal = {
   // TODO: figure out the API for cross-renderer implementation.
   implementation: any,
 };
+
+export type RefObject = {|
+  value: any,
+|};