If you pass a string to multiply(), VS Code will show you an error by underlining the problematic part of your code:

Hover over it with the mouse, and VS Code will tell you more:

Now, regarding TypeScript errors, sometimes they are a bit cryptic. Not in this case. But there is a VS Code extension that helps you by giving actionable information, and it’s called Pretty TypeScript Errors.

Install that, you’ll see different error messages:

This is what happens in the editor.

Lessons in this unit:

0:	Introduction
1:	Your first TypeScript program
2:	Types
3:	Typing functions
4:	▶︎ The editor helps you with type errors
5:	Running TypeScript code
6:	Valid types
7:	Type aliases and interfaces
8:	Union types
9:	Typing arrays with generics
10:	The DX of editing TypeScript
11:	There's more...
12:	TypeScript declare a type that can be a string or array of strings
13:	TypeScript, disable checks for `declared but its value is never read`
14:	Object destructuring with types in TypeScript
15:	TypeScript Tutorial
16:	Zod: Type-Safe Schema Validation for TypeScript
17:	How I fixed some trouble importing types in .d.ts files