TypeScript Is Not Enough: Why We Need Runtime Validation
## The Type Safety Illusion
We have been lulled into a false sense of security. TypeScript gives us compile-time guarantees, but the moment data crosses a boundary—an API call, a form submission, a database query—those guarantees vanish.
### The Problem
Consider this code:
```typescript
interface User {
id: string;
email: string;
age: number;
}
async function getUser(id: string): Promise {
const response = await fetch(`/api/users/${id}`);
return response.json(); // Trust issues
}
```
That `return response.json()` is a lie. You are telling TypeScript "trust me, this is a User" when you have no idea what the API actually returned.
### The Solution
Use runtime validation. Zod, Valibot, ArkType—pick one. Validate at every boundary.
```typescript
const UserSchema = z.object({
id: z.string(),
email: z.string().email(),
age: z.number().int().positive(),
});
async function getUser(id: string): Promise {
const response = await fetch(`/api/users/${id}`);
return UserSchema.parse(await response.json());
}
```
Yes, it is more code. Yes, it is worth it. Your 3 AM self will thank you.