Avoid using an array index as key prop, prefer unique ID

react/README.md

@@ -279,6 +279,26 @@
   <div />
   ```
 
+  - Avoid using an array index as `key` prop, prefer a unique ID. ([why?](https://medium.com/@robinpokorny/index-as-a-key-is-an-anti-pattern-e0349aece318))
+
+  ```jsx
+  // bad
+  {todos.map((todo, index) =>
+    <Todo
+      {...todo}
+      key={index}
+    />
+  )}
+
+  // good
+  {todos.map((todo) =>
+    <Todo
+      {...todo}
+      key={todo.id}
+    />
+  )}
+  ```
+
 ## Parentheses
 
   - Wrap JSX tags in parentheses when they span more than one line. eslint: [`react/wrap-multilines`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/wrap-multilines.md)