Describe how TypeScript checks JavaScript files (#6238)

src/data/roadmaps/typescript/content/100-typescript/101-ts-js-interoperability.md

@@ -5,3 +5,24 @@ TypeScript and JavaScript have full interoperability, meaning you can use TypeSc
 You can use JavaScript libraries in TypeScript projects by either including the JavaScript files directly or using type definitions for the library. Type definitions provide type information for JavaScript libraries, making it easier to use them in TypeScript.
 
 On the other hand, you can use TypeScript code in JavaScript projects by simply compiling the TypeScript code into JavaScript. The generated JavaScript code can be used in any JavaScript environment, and it will work the same way as regular JavaScript code.
+
+TypeScript's compiler also supports type checking for plain JavaScript code by adding the `// @ts-check` comment at the top of a file. This allows the compiler to validate types by inspecting the JSDoc comments:
+
+```typescript
+// @ts-check
+
+/**
+ * Adds two numbers together.
+ * @param {number} a - The first number.
+ * @param {number} b - The second number.
+ * @returns {number} The sum of the two numbers.
+ */
+function add(a, b) {
+  return a + b;
+}
+```
+
+Learn more from the following links:
+
+- [@article@Type Checking JavaScript Files](https://www.typescriptlang.org/docs/handbook/type-checking-javascript-files.html)
+- [@video@Using JavaScript in TypeScript](https://youtu.be/AZhZlEbBaB4)