Add SuspenseList to react-is

Author: Brian Vaughn

packages/react-is/src/ReactIs.js

@@ -72,6 +72,9 @@ export const Portal = REACT_PORTAL_TYPE;
 export const Profiler = REACT_PROFILER_TYPE;
 export const StrictMode = REACT_STRICT_MODE_TYPE;
 export const Suspense = REACT_SUSPENSE_TYPE;
+export const SuspenseList = __EXPERIMENTAL__
+  ? REACT_SUSPENSE_LIST_TYPE
+  : undefined;
 
 export {isValidElementType};
 
@@ -142,3 +145,10 @@ export function isStrictMode(object: any) {
 export function isSuspense(object: any) {
   return typeOf(object) === REACT_SUSPENSE_TYPE;
 }
+export function isSuspenseList(object: any) {
+  if (__EXPERIMENTAL__) {
+    return typeOf(object) === REACT_SUSPENSE_LIST_TYPE;
+  } else {
+    return false;
+  }
+}

packages/react-is/src/__tests__/ReactIs-test.js

@@ -186,6 +186,16 @@ describe('ReactIs', () => {
     expect(ReactIs.isSuspense(<div />)).toBe(false);
   });
 
+  // @gate experimental
+  it('should identify suspense list', () => {
+    expect(ReactIs.isValidElementType(React.SuspenseList)).toBe(true);
+    expect(ReactIs.typeOf(<React.SuspenseList />)).toBe(ReactIs.SuspenseList);
+    expect(ReactIs.isSuspenseList(<React.SuspenseList />)).toBe(true);
+    expect(ReactIs.isSuspenseList({type: ReactIs.SuspenseList})).toBe(false);
+    expect(ReactIs.isSuspenseList('React.SuspenseList')).toBe(false);
+    expect(ReactIs.isSuspenseList(<div />)).toBe(false);
+  });
+
   it('should identify profile root', () => {
     expect(ReactIs.isValidElementType(React.Profiler)).toBe(true);
     expect(