fix logic for default of used root implementation

Author: eps1lon

src/__tests__/render.js

@@ -114,7 +114,7 @@ test('throws if `legacyRoot: false` is used with an incomaptible version', () =>
   } else {
     // eslint-disable-next-line jest/no-conditional-expect -- yes, jest still doesn't support conditional tests
     expect(performConcurrentRender).toThrowError(
-      `"Attempted to use concurrent React with \`react-dom@${ReactDOM.version}\`. Be sure to use the \`next\` or \`experimental\` release channel (https://reactjs.org/docs/release-channels.html)."`,
+      `Attempted to use concurrent React with \`react-dom@${ReactDOM.version}\`. Be sure to use the \`next\` or \`experimental\` release channel (https://reactjs.org/docs/release-channels.html).`,
     )
   }
 })

src/pure.js

@@ -139,7 +139,7 @@ function render(
   {
     container,
     baseElement = container,
-    legacyRoot,
+    legacyRoot = typeof ReactDOM.createRoot !== 'function',
     queries,
     hydrate = false,
     wrapper,
@@ -157,10 +157,7 @@ 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 createRootImpl =
-      legacyRoot === true || typeof ReactDOM.createRoot !== 'function'
-        ? createLegacyRoot
-        : createConcurrentRoot
+    const createRootImpl = legacyRoot ? createLegacyRoot : createConcurrentRoot
     root = createRootImpl(container, {hydrate})
 
     mountedRootEntries.push({container, root})