React fiber support

app/react/src/client/preview/__snapshots__/element_check.test.js.snap

@@ -0,0 +1,13 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`element_check.utils.flattenList should flatten a deep nested list 1`] = `
+Array [
+  1,
+  2,
+  3,
+  4,
+  5,
+  6,
+  7,
+]
+`;

app/react/src/client/preview/element_check.js

@@ -0,0 +1,49 @@
+import React from 'react';
+
+// return true if the element is renderable with react fiber
+export const isValidFiberElement = element =>
+  typeof element === 'string' || typeof element === 'number' || React.isValidElement(element);
+
+// input: [1, 2, [3, 4, [5, 6, [7]]]]
+// output: [ 1, 2, 3, 4, 5, 6, 7 ]
+export const flattenList = list =>
+  list.reduce((array, element) => {
+    const newElement = Array.isArray(element) ? flattenList(element) : [element];
+
+    return [...array, ...newElement];
+  }, []);
+
+export const isPriorToFiber = version => {
+  const [majorVersion] = version.split('.');
+
+  return Number(majorVersion) < 16;
+};
+
+// accepts an element and return true if renderable else return false
+const isReactRenderable = element => {
+  // storybook is running with a version prior to fiber,
+  // run a simple check on the element
+  if (isPriorToFiber(React.version)) {
+    return React.isValidElement(element);
+  }
+
+  // the element is not an array, check if its a fiber renderable element
+  if (!Array.isArray(element)) {
+    return isValidFiberElement(element);
+  }
+
+  // the element is in fact a list of elements (array),
+  // loop on its elements to see if its ok to render them
+  const elementsList = element.map(isReactRenderable);
+
+  // flatten the list of elements (possibly deep nested)
+  const flatList = flattenList(elementsList);
+
+  // keep only invalid elements
+  const invalidElements = flatList.filter(elementIsRenderable => elementIsRenderable === false);
+
+  // it's ok to render this list if there is no invalid elements inside
+  return !invalidElements.length;
+};
+
+export default isReactRenderable;

app/react/src/client/preview/element_check.test.js

@@ -0,0 +1,98 @@
+import React from 'react';
+import isReactRenderable, {
+  isValidFiberElement,
+  flattenList,
+  isPriorToFiber,
+} from './element_check';
+
+describe('element_check.utils.isValidFiberElement', () => {
+  it('should accept to render a string', () => {
+    const string = 'react is awesome';
+
+    expect(isValidFiberElement(string)).toBe(true);
+  });
+
+  it('should accept to render a number', () => {
+    const number = 42;
+
+    expect(isValidFiberElement(number)).toBe(true);
+  });
+
+  it('should accept to render a valid React element', () => {
+    const element = <button>Click me</button>;
+
+    expect(isValidFiberElement(element)).toBe(true);
+  });
+
+  it("shouldn't accept to render an arbitrary object", () => {
+    const object = { key: 'bee bop' };
+
+    expect(isValidFiberElement(object)).toBe(false);
+  });
+
+  it("shouldn't accept to render a function", () => {
+    const noop = () => {};
+
+    expect(isValidFiberElement(noop)).toBe(false);
+  });
+
+  it("shouldn't accept to render undefined", () => {
+    expect(isValidFiberElement(undefined)).toBe(false);
+  });
+});
+
+describe('element_check.utils.flattenList', () => {
+  it('should flatten a deep nested list', () => {
+    const deepNestedList = [1, 2, [3, 4, [5, 6, [7]]]];
+
+    expect(flattenList(deepNestedList)).toMatchSnapshot();
+  });
+});
+
+describe('element_check.utils.isPriorToFiber', () => {
+  it('should return true if React version is prior to Fiber (< 16)', () => {
+    const oldVersion = '0.14.5';
+    const version = '15.5.4';
+
+    expect(isPriorToFiber(oldVersion)).toBe(true);
+    expect(isPriorToFiber(version)).toBe(true);
+  });
+
+  it('should return false if React version is using Fiber features (>= 16)', () => {
+    const alphaVersion = '16.0.0-alpha.13';
+    const version = '18.3.1';
+
+    expect(isPriorToFiber(alphaVersion)).toBe(false);
+    expect(isPriorToFiber(version)).toBe(false);
+  });
+});
+
+describe('element_check.isReactRenderable', () => {
+  const string = 'yo';
+  const number = 1337;
+  const element = <span>what's up</span>;
+  const array = [string, number, element];
+  const object = { key: null };
+
+  it('allows rendering React elements only prior to React Fiber', () => {
+    // mutate version for the purpose of the test
+    React.version = '15.5.4';
+
+    expect(isReactRenderable(string)).toBe(false);
+    expect(isReactRenderable(number)).toBe(false);
+    expect(isReactRenderable(element)).toBe(true);
+    expect(isReactRenderable(array)).toBe(false);
+    expect(isReactRenderable(object)).toBe(false);
+  });
+
+  it('allows rendering string, numbers, arrays and React elements with React Fiber', () => {
+    // mutate version for the purpose of the test
+    React.version = '16.0.0-alpha.13';
+
+    expect(isReactRenderable(string)).toBe(true);
+    expect(isReactRenderable(number)).toBe(true);
+    expect(isReactRenderable(element)).toBe(true);
+    expect(isReactRenderable(array)).toBe(true);
+    expect(isReactRenderable(object)).toBe(false);
+  });
+});

app/react/src/client/preview/render.js

@@ -3,6 +3,7 @@
 import React from 'react';
 import ReactDOM from 'react-dom';
 import { stripIndents } from 'common-tags';
+import isReactRenderable from './element_check';
 import ErrorDisplay from './error_display';
 
 // check whether we're running on node/browser
@@ -83,6 +84,17 @@ export function renderMain(data, storyStore) {
     return renderError(error);
   }
 
+  if (!isReactRenderable(element)) {
+    const error = {
+      title: `Expecting a valid React element from the story: "${selectedStory}" of "${selectedKind}".`,
+      description: stripIndents`
+         Seems like you are not returning a correct React element from the story.
+         Could you double check that?
+       `,
+    };
+    return renderError(error);
+  }
+
   ReactDOM.render(element, rootEl);
   return null;
 }