Fix broken links in useReducer documentation (#5882)

Author: slieschke

src/content/reference/react/useReducer.md

@@ -52,7 +52,7 @@ function MyComponent() {
 #### Caveats {/*caveats*/}
 
 * `useReducer` is a Hook, so you can only call it **at the top level of your component** or your own Hooks. You can't call it inside loops or conditions. If you need that, extract a new component and move the state into it.
-* In Strict Mode, React will **call your reducer and initializer twice** in order to [help you find accidental impurities.](#my-initializer-or-updater-function-runs-twice) This is development-only behavior and does not affect production. If your reducer and initializer are pure (as they should be), this should not affect your logic. The result from one of the calls is ignored.
+* In Strict Mode, React will **call your reducer and initializer twice** in order to [help you find accidental impurities.](#my-reducer-or-initializer-function-runs-twice) This is development-only behavior and does not affect production. If your reducer and initializer are pure (as they should be), this should not affect your logic. The result from one of the calls is ignored.
 
 ---
 
@@ -992,7 +992,7 @@ function reducer(state, action) {
 }
 ```
 
-You mutated an existing `state` object and returned it, so React ignored the update. To fix this, you need to ensure that you're always [_replacing_ objects and arrays in state instead of _mutating_ them](#updating-objects-and-arrays-in-state):
+You mutated an existing `state` object and returned it, so React ignored the update. To fix this, you need to ensure that you're always [updating objects in state](/learn/updating-objects-in-state) and [updating arrays in state](/learn/updating-arrays-in-state) instead of mutating them:
 
 ```js {4-8,11-15}
 function reducer(state, action) {
@@ -1100,7 +1100,7 @@ function reducer(state, action) {
 }
 ```
 
-Because React calls your reducer function twice, you'll see the todo was added twice, so you'll know that there is a mistake. In this example, you can fix the mistake by [replacing the array instead of mutating it](#updating-objects-and-arrays-in-state):
+Because React calls your reducer function twice, you'll see the todo was added twice, so you'll know that there is a mistake. In this example, you can fix the mistake by [replacing the array instead of mutating it](/learn/updating-arrays-in-state#adding-to-an-array):
 
 ```js {4-11}
 function reducer(state, action) {