TypeScript Types and Interfaces

End-of-lesson check

15 questions · take it digitally for instant feedback at tendril.neural-forge.io/learn/quiz/end-progx-ts-interfaces-creators

1. Which TypeScript feature is specifically recommended for defining object shapes that will be implemented by classes?

   1. A generic
   2. An interface
   3. A tuple
   4. A type alias

2. You need to define a type that can be exactly one of three specific string values. Which approach should you use?

   1. A tuple type
   2. An interface with optional properties
   3. A union type using type alias
   4. A mapped type

3. What does the question mark (?) indicate when used in an interface property definition?

   1. The property is optional and may not exist
   2. The property cannot be modified after initialization
   3. The property must be a string
   4. The property is private to the interface

4. You want to ensure that once an object's property is set, it cannot be changed anywhere in your code. Which modifier should you use?

   1. readonly
   2. private
   3. static
   4. const

5. You have two interfaces with overlapping properties and want to combine them into one type. What approach works best?

   1. Copy all properties manually
   2. Use a tuple to hold both
   3. Use two separate variables
   4. Create a third interface that extends both

6. A function receives a parameter of type 'string | number'. What values is this parameter allowed to have?

   1. Only numbers
   2. Only strings
   3. Neither strings nor numbers
   4. Either a string or a number, but not both at once

7. In a discriminated union, what is the 'discriminant' property used for?

   1. To combine two interfaces
   2. To make a property readonly
   3. To uniquely identify which union member a value belongs to
   4. To make properties optional

8. What is a tuple in TypeScript?

   1. A special kind of class
   2. A way to combine interfaces
   3. An array with a fixed number of elements where each position has a specific type
   4. A type that can be any value

9. What is structural typing in TypeScript?

   1. A way to structure your code files
   2. A type of loop
   3. Type compatibility based on an object's shape rather than its name
   4. A method for creating interfaces

10. You notice the exact same object shape appears in three different places in your code. What should you do?

    1. Use a different shape each time
    2. Hoist the shape into an interface and reuse it
    3. Copy and paste the shape three times
    4. Use a type alias with any for flexibility

11. Which statement about mapped types is true?

    1. They map DOM events to handlers
    2. They cannot use interfaces
    3. They are only used with classes
    4. They transform existing types by applying a pattern to each property

12. What advantage do interfaces provide over inline type definitions?

    1. Interfaces can be extended and reused across your codebase
    2. Interfaces automatically generate documentation
    3. Interfaces run faster
    4. Interfaces can be compiled to any language

13. When modeling a domain where you have different 'kinds' of entities that share some properties but differ in others, what should you use?

    1. Multiple unrelated interfaces
    2. A tuple for each entity
    3. A single large interface with all properties
    4. A discriminated union with a shared discriminant property

14. Why does modeling your domain with interfaces and unions provide 'safety for free'?

    1. Because TypeScript is open source
    2. Because function parameters and return types get type checking when you reuse well-defined types
    3. Because the compiler automatically fixes bugs
    4. Because interfaces are faster than types

15. What happens if you try to assign an object to a variable with an interface type, but the object is missing an optional property?

    1. The optional property is automatically added
    2. The object is mutated to include the property
    3. A compile-time error occurs
    4. It works fine—optional properties can be missing