Improve documentation and fix instruction clarity

- Fix async/await README to say "return" instead of "log" to match tests
- Add note about import { type X } syntax for Node.js TypeScript support
- Add TypeScript Playground tips for mapped types and conditional types

Author: kentcdodds

exercises/02.async-await/01.problem.linear-flow/README.mdx

@@ -8,15 +8,15 @@ async/await. This will make the code much more readable!
 1. Create an `async` function called `loadUserData`
 2. Use `await` to fetch the user
 3. Use `await` to fetch the orders
-4. Log both results
+4. Return an object with both `user` and `orders`
 
 💰 Async/await syntax:
 
 ```ts
 async function loadUserData() {
 	const user = await fetchUser()
 	const orders = await fetchOrders(user.id)
-	console.log(user, orders)
+	return { user, orders }
 }
 ```
 

exercises/04.modules/01.problem.import-export/README.mdx

@@ -17,9 +17,16 @@ export type User = { ... }
 export type Product = { ... }
 
 // index.ts
-import { User, Product } from './types.ts'
+import { type User, type Product } from './types.ts'
 ```
 
+<callout-info>
+	When importing **types only** (not values), use `import { type X }` syntax.
+	This tells TypeScript (and Node.js) that these imports are purely for type
+	checking and should be erased at runtime. This is required when running
+	TypeScript natively with Node.js.
+</callout-info>
+
 📜 [MDN - ES Modules](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules)
 
 🐨 Once you've completed the exercise, run `node index.ts` in the playground to test your work!

exercises/08.mapped-types/01.problem.creating-mapped-types/README.mdx

@@ -27,4 +27,8 @@ type RemoveOptional<T> = {
 
 📜 [TypeScript Handbook - Mapped Types](https://www.typescriptlang.org/docs/handbook/2/mapped-types.html)
 
+💰 Try experimenting with mapped types in the
+[TypeScript Playground](https://www.typescriptlang.org/play) - hover over type
+aliases to see how TypeScript evaluates them!
+
 🐨 Once you've completed the exercise, run `node index.ts` in the playground to test your work!

exercises/09.conditional-types/01.problem.basic-conditionals/README.mdx

@@ -24,4 +24,8 @@ type IsArray<T> = T extends any[] ? true : false
 
 📜 [TypeScript Handbook - Conditional Types](https://www.typescriptlang.org/docs/handbook/2/conditional-types.html)
 
+💰 Conditional types can be tricky to understand. Try experimenting in the
+[TypeScript Playground](https://www.typescriptlang.org/play) - hover over type
+aliases to see how TypeScript evaluates each step of the condition!
+
 🐨 Once you've completed the exercise, run `node index.ts` in the playground to test your work!

exercises/09.conditional-types/02.problem.basic-infer/README.mdx

@@ -44,4 +44,8 @@ T extends (...args: any[]) => infer R ? R : never
 
 📜 [TypeScript Handbook - Inferring Within Conditional Types](https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#inferring-within-conditional-types)
 
+💰 The [TypeScript Playground](https://www.typescriptlang.org/play) is especially
+helpful for understanding `infer`. Hover over type aliases to see how TypeScript
+infers the captured type variables!
+
 🐨 Once you've completed the exercise, run `node index.ts` in the playground to test your work!

exercises/09.conditional-types/03.problem.infer-keyword/README.mdx

@@ -48,4 +48,8 @@ type LastElement<T> = T extends [...infer _, infer L] ? L : never
 
 📜 [TypeScript Handbook - Inferring Within Conditional Types](https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#inferring-within-conditional-types)
 
+💰 Use the [TypeScript Playground](https://www.typescriptlang.org/play) to
+experiment with different tuple patterns. Hover over your type aliases to see
+how TypeScript evaluates each step!
+
 🐨 Once you've completed the exercise, run `node index.ts` in the playground to test your work!