docs: update extend matcher (#3123)

Co-authored-by: Vladimir Sheremet <sleuths.slews0s@icloud.com>
vitest-dev · Apr 5, 2023 · 74b7ab0 · 74b7ab0
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diff --git a/docs/api/expect.md b/docs/api/expect.md
@@ -1275,23 +1275,25 @@ type Awaitable<T> = T | PromiseLike<T>
 
   This function is compatible with Jest's `expect.extend`, so any library that uses it to create custom matchers will work with Vitest.
 
-  If you are using TypeScript, you can extend default Matchers interface with the code bellow:
+  If you are using TypeScript, you can extend default `Matchers` interface in an ambient declaration file (e.g: `vitest.d.ts`) with the code below:
 
   ```ts
   interface CustomMatchers<R = unknown> {
     toBeFoo(): R
   }
 
-  declare global {
-    namespace Vi {
-      interface Assertion extends CustomMatchers {}
-      interface AsymmetricMatchersContaining extends CustomMatchers {}
-    }
+  declare namespace Vi {
+    interface Assertion extends CustomMatchers {}
+    interface AsymmetricMatchersContaining extends CustomMatchers {}
 
     // Note: augmenting jest.Matchers interface will also work.
   }
   ```
 
+  ::: warning
+  Don't forget to include the ambient declaration file in your `tsconfig.json`.
+  :::
+
   :::tip
   If you want to know more, checkout [guide on extending matchers](/guide/extending-matchers).
   :::
diff --git a/docs/guide/extending-matchers.md b/docs/guide/extending-matchers.md
@@ -23,23 +23,25 @@ expect.extend({
 })
 ```
 
-If you are using TypeScript, you can extend default Matchers interface with the code bellow:
+If you are using TypeScript, you can extend default Matchers interface in an ambient declaration file (e.g: `vitest.d.ts`) with the code below:
 
 ```ts
 interface CustomMatchers<R = unknown> {
   toBeFoo(): R
 }
 
-declare global {
-  namespace Vi {
-    interface Assertion extends CustomMatchers {}
-    interface AsymmetricMatchersContaining extends CustomMatchers {}
-  }
+declare namespace Vi {
+  interface Assertion extends CustomMatchers {}
+  interface AsymmetricMatchersContaining extends CustomMatchers {}
 
   // Note: augmenting jest.Matchers interface will also work.
 }
 ```
 
+::: warning
+Don't forget to include the ambient declaration file in your `tsconfig.json`.
+:::
+
 The return value of a matcher should be compatible with the following interface:
 
 ```ts