fix(curriculum): clarify that replace() returns a new string in JS lesson (#61730)

Co-authored-by: Huyen Nguyen <25715018+huyenltnguyen@users.noreply.github.com>
Co-authored-by: Ilenia M <nethleen@gmail.com>

curriculum/challenges/english/25-front-end-development/lecture-working-with-string-modification-methods/67326c29dcd98fc5ecc49779.md

@@ -11,7 +11,7 @@ In JavaScript, there are many scenarios where you may need to replace a portion
 
 For instance, you might need to update user information in a URL, change the formatting of dates, or correct errors in user-generated content.
 
-The `replace()` method in JavaScript allows you to find a specified value (like a word or character) in a string and replace it with another value.
+The `replace()` method in JavaScript allows you to find a specified value (like a word or character) in a string and replace it with another value. The method returns a new string with the replacement and leaves the original unchanged because JavaScript strings are immutable.
 
 Here is the basic syntax:
 

curriculum/challenges/english/25-front-end-development/review-javascript-strings/6723c1946e4cd7909a836bb4.md

@@ -98,7 +98,7 @@ const text = "HELLO, WORLD!"
 console.log(text.toLowerCase()); // "hello, world!"
 ```
 
-- **The `replace()` Method**: This method is used to find a specified value (like a word or character) in a string and replace it with another value.
+- **The `replace()` Method**: This method allows you to find a specified value (like a word or character) in a string and replace it with another value. The method returns a new string with the replacement and leaves the original unchanged because JavaScript strings are immutable.
 
 ```js
 const text = "I like cats";

curriculum/challenges/english/25-front-end-development/review-javascript/6723d3cfdd0717d3f1bf27e3.md

@@ -300,7 +300,7 @@ const text = "HELLO, WORLD!"
 console.log(text.toLowerCase()); // "hello, world!"
 ```
 
-- **The `replace()` Method**: This method is used to find a specified value (like a word or character) in a string and replace it with another value.
+- **The `replace()` Method**: This method allows you to find a specified value (like a word or character) in a string and replace it with another value. The method returns a new string with the replacement and leaves the original unchanged because JavaScript strings are immutable.
 
 ```js
 const text = "I like cats";