concurrent: false -> legacyRoot: true

Author: eps1lon

src/__tests__/render.js

@@ -102,10 +102,10 @@ test('flushes useEffect cleanup functions sync on unmount()', () => {
   expect(spy).toHaveBeenCalledTimes(1)
 })
 
-test('throws if `concurrent` is used with an incomaptible version', () => {
+test('throws if `legacyRoot: false` is used with an incomaptible version', () => {
   const isConcurrentReact = typeof ReactDOM.createRoot === 'function'
 
-  const performConcurrentRender = () => render(<div />, {concurrent: true})
+  const performConcurrentRender = () => render(<div />, {legacyRoot: false})
 
   // eslint-disable-next-line jest/no-if -- jest doesn't support conditional tests
   if (isConcurrentReact) {

src/pure.js

@@ -139,7 +139,7 @@ function render(
   {
     container,
     baseElement = container,
-    concurrent = false,
+    legacyRoot,
     queries,
     hydrate = false,
     wrapper,
@@ -157,8 +157,11 @@ function render(
   let root
   // eslint-disable-next-line no-negated-condition -- we want to map the evolution of this over time. The root is created first. Only later is it re-used so we don't want to read the case that happens later first.
   if (!mountedContainers.has(container)) {
-    const createRoot = concurrent ? createConcurrentRoot : createLegacyRoot
-    root = createRoot(container, {hydrate})
+    const createRootImpl =
+      legacyRoot === true || typeof ReactDOM.createRoot !== 'function'
+        ? createLegacyRoot
+        : createConcurrentRoot
+    root = createRootImpl(container, {hydrate})
 
     mountedRootEntries.push({container, root})
     // we'll add it to the mounted containers regardless of whether it's actually

types/index.d.ts

@@ -37,6 +37,11 @@ export interface RenderOptions<
   container?: Container
   baseElement?: Element
   hydrate?: boolean
+  /**
+   * Set to `true` if you want to force synchronous `ReactDOM.render`.
+   * Otherwise `render` will default to concurrent React if available.
+   */
+  legacyRoot?: boolean
   queries?: Q
   wrapper?: React.ComponentType
 }