Add measurement of React tree size

src/tasks/preset/client.tsx

@@ -2,6 +2,7 @@ import ReactDOM from 'react-dom';
 import ReactDOMServer from 'react-dom/server';
 import {
   RunStaticTaskArgs,
+  RunStaticTaskArgsWithReactRoot,
   RunTimedTaskArgs,
   StaticTask,
   TaskGroup,
@@ -123,10 +124,59 @@ const completeRender: TimedTask = timedTask({
   },
 });
 
+interface Fiber {
+  // Singly Linked List Tree Structure.
+  // Full type here https://github.com/facebook/react/blob/master/packages/react-reconciler/src/ReactInternalTypes.js
+  child: Fiber | null;
+  sibling: Fiber | null;
+}
+
+export function traverse(rootNode: Fiber, callback: (node: Fiber) => void) {
+  function walk(node: Fiber) {
+    // First call the callback on the node.
+    callback(node);
+
+    if (!node.child && !node.sibling) {
+      return;
+    }
+
+    // Then recursively call the walk function on each child and sibling.
+    node.child && walk(node.child);
+    node.sibling && walk(node.sibling);
+  }
+
+  walk(rootNode);
+}
+
+const reactFiberNodeCount: StaticTask = staticTask({
+  name: 'React Fiber node count',
+  description: `
+    The number of React Elements or internal objects ("fibers") that hold information about the component tree state.
+  `,
+  run: async ({ getElement, container }: RunStaticTaskArgsWithReactRoot): Promise<string> => {
+    ReactDOM.render(getElement(), container);
+
+    const fiberRoot = container?._reactRootContainer?._internalRoot?.current;
+
+    let count = 0;
+    fiberRoot && traverse(fiberRoot, () => count++);
+
+    return String(count);
+  },
+});
+
 const group: TaskGroup = {
   groupId: 'Client',
   name: 'Client 👩‍💻',
-  tasks: [render, reRender, hydrate, domElementCount, domElementCountWithoutSvg, completeRender],
+  tasks: [
+    render,
+    reRender,
+    hydrate,
+    domElementCount,
+    domElementCountWithoutSvg,
+    completeRender,
+    reactFiberNodeCount,
+  ],
 };
 
 export default group;

src/types.ts

@@ -10,11 +10,18 @@ type BaseTask = {
   description: string;
 };
 
+interface Container extends HTMLElement {
+  _reactRootContainer?: any;
+}
+
 export type RunStaticTaskArgs = {
   getElement: () => React.ReactElement;
   container: HTMLElement;
 };
-
+export type RunStaticTaskArgsWithReactRoot = {
+  getElement: () => React.ReactElement;
+  container: Container;
+};
 export type StaticTask = BaseTask & {
   scale?: string;
   type: 'static';