diff --git a/contents/string/capitalize-a-string.md b/contents/string/capitalize-a-string.md
index bbcd9aa4..e511968c 100644
--- a/contents/string/capitalize-a-string.md
+++ b/contents/string/capitalize-a-string.md
@@ -19,13 +19,13 @@ const capitalize = (str) => str.replace(/^([a-z])/, (first) => first.toUpperCase
 **TypeScript version**
 
 ```js
-const capitalize = (str: string): string => `${str.charAt(0).toUpperCase()}${str.slice(1)}`;
+const capitalize1 = <T extends string,>(str: T) => `${str.charAt(0).toUpperCase()}${str.slice(1)}` as Capitalize<T>;
 
 // Or
-const capitalize = ([first, ...rest]: string): string => `${first.toUpperCase()}${rest.join('')}`;
+const capitalize2 = <T extends string,>([first, ...rest]: T) => `${first.toUpperCase()}${rest.join('')}` as Capitalize<T>;
 
 // Or
-const capitalize = (str: string): string => str.replace(/^([a-z])/, (first) => first.toUpperCase());
+const capitalize3 = <T extends string,>(str: T) => str.replace(/^([a-z])/, (first) => first.toUpperCase()) as Capitalize<T>;
 ```
 
 **Examples**