✏️ 3.2.0.12 TypeScript Practice Exercises

Goal: Practice the TypeScript concepts from the earlier lessons before starting the project. Work through as many of these as you can on your own. These exercises are for practice - there's no single right answer for most of them.

Set up a small TypeScript project (or use the one you created in the Setting Up TypeScript lesson) to try these out with ts-node.

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Exercise 1: Type Annotations and Inference

1. Declare a const variable for each of these values without annotations. Hover over each in VS Code to see what TypeScript infers:

   • Your name (note: avoid naming your variable name to prevent conflicts with built-in properties)
   • Your age
   • Whether you prefer dark mode (true or false)
   • A list of your three favorite programming languages

2. Now declare the same four values using let. What changes about the inferred types?

3. Declare an empty array for a shopping list. What does TypeScript infer? Fix it by adding an explicit annotation.

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Exercise 2: Object Types

1. Define a type called Movie with the following properties:

   • title - a string
   • director - a string
   • year - a number
   • genre - one of: "action", "comedy", "drama", "horror", "sci-fi" (use a separate type alias for this)
   • rating - a number (optional)

2. Create at least three Movie objects that satisfy this type. Make sure at least one has a rating and at least one doesn't.

3. Create a Movie[] array containing your three movies.

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Exercise 3: Typed Functions

Write the following functions with full type annotations on parameters and return types:

1. getTitle(movie: Movie): string - returns the title of a movie

2. filterByGenre(movies: Movie[], genre: Genre): Movie[] - returns all movies of a given genre (use the Genre type you created above)

3. createMovie(title: string, director: string, year: number, genre: Genre): Movie - creates and returns a new Movie object with no rating

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Exercise 4: Literal Union Types

1. Create a Priority type that can be "low", "medium", "high", or "critical".

2. Write a function getPriorityLabel(priority: Priority): string that returns a descriptive label for each level (e.g., "Low priority", "Critical - address immediately"). Use a switch or if/else chain.

3. Call getPriorityLabel with "urgent" instead of a valid priority. What does TypeScript say?

4. Create a Status type that can be "active" or "inactive". Declare a variable of that type, reassign it to the other valid value, then try to assign it "pending". What error do you get? (Note: avoid naming your variable status to prevent conflicts with built-in properties.)