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TYPELAND QUIZ RESULTS
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Student Name: Donovan Tong
Quiz Started: March 19, 2026 at 02:15:31 PM
Quiz Completed: March 19, 2026 at 02:52:34 PM
Duration: 37 minutes 3 seconds
Total Questions: 20

Grading Rubric: 
multiple choice: 1 point
short answer: 2 points
code completion: 3 points

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Question 1:
Which declaration allows reassignment but not redeclaration in the same scope?

Answer:
let

Points: 1/1

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Question 2:
List all the Typescript primitive types that we have gone over so far.

Answer:
Symbol, undefined, null, void, never

Points: 1/2
// Good job on remembering the lesser known ones,
// but you forgot about the basic ones like string, number, Boolean, and bigInt

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Question 3:
Fill in types so the code compiles without 'any' and noImplicitAny errors
Correct the provided code.

Answer:
const item = {
let id: number = 42;
let name: string = "Widget";
let active: boolean = true;
}

function format(item): string {
  return `${item.id}: ${item.name} (${item.active})`;
}

Points: 2/3
// You set the types of the item properties, but how is the format function
// supposed to know what type item is supposed to be?

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Question 4:
When should we favor using undefined instead of null in TypeScript?

Answer:
When a variable is intentionally left uninitialized

Points: 1/1

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Question 5:
Which syntax defines a type alias for a union of string literals?

Answer:
type Size = 'S' | 'M' | 'L'

Points: 1/1

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Question 6:
Explain the difference between a type alias and an interface in TypeScript in one sentence.

Answer:
Type alias is another way to rename a type in order to improve readability but are more general. Interfaces only define shapes for classes.

Points: 2/2
// Good job

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Question 7:
Create a type alias 'ID' that accepts either a string or a number and write a function 'getById' signature that accepts id: ID and returns Promise<object | null>.

Answer:
type ID = string | number;
const getById(id:ID) = {
     return Promise<object | null>
}

Points: 1/3
// making a function should start with the keyword function, not const
// Also Promise<object | null> is a type, not something that can physically
// be returned by the function. 

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Question 8:
Which function signature correctly types a function that takes a number and returns a number?

Answer:
function f(x: number): number {}

Points: 1/1

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Question 9:
Explain the difference between extends and implements in TypeScript classes and when you would use each one.

Answer:
Extends can add more methods to the interface, whereas implements uses the interfaces as is with the current defined methods.

Points: 1/2
// Good definitions, but you never explained when to use each one

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Question 10:
What does the 'void' return type indicate and when would you use 'never' instead?

Answer:
Void is when nothing will be returned within the scope of the method/function. Never is defining a case to prevent it from happening.

Points: 1/2
// Goode definition for Void, and Never defines something that should never happen
// You didn't explain when you would use Never, you only explained what it was. 

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Question 11:
Which type annotation declares an array of strings?

Answer:
Both A and B

Points: 1/1

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Question 12:
Define a tuple type 'ProductTuple' for [id: number, name: string, inStock: boolean] and create a variable 'p' of that type.

Answer:
type ProductTuple = [id: number, name: string, instock: boolean];
const p: ProductTuple = [id: 6221, name: Sheet, instock: True];

Points: 3/3
// You don't need to name the properties in the Tuple type, you could
// just write type ProductTuple = [number, string, boolean]; 
// You also forgot to put "" around Sheet, and True should be lowercase 
// But I won't dock points for that because you were really close. 

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Question 13:
The following code fails type checking. Fix the types only

Answer:
const product = {
  id: "100",
  name: "Socks",
  price: 9.99
};

function printPrice(p: { id: string; name: string; price: number }) {
  console.log(p.price);
}

printPrice(product);

Points: 3/3

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Question 14:
Explain why one would explicitly declare an object type when TypeScript can often infer it from the assigned value.

Answer:
In order to ensure that any instance of that object is not reassigned incorrectly or mutated incorrectly.

Points: 0/2
// Declaring an object type mainly helps with readability and code maintainability 
// TypeScript will infer the type of an object that wasn't given one when it is first assigned
// a value, and then after that will warn you if you try to assign it to a value of a
// different type. 

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Question 15:
Which keyword enforces that a class implements a contract shape?

Answer:
implements

Points: 1/1

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Question 16:
Write a class 'User' that implements this interface and includes a constructor

Answer:
interface IUser {
  id: number;
  name: string;
  isActive?: boolean;
  greet(): string;
}

class User = {
  constructor(id: number, name: string, isActive?: boolean) = {
    this.id = id;
    this.name = name;
    this.isActive = isActive;
  }
  greet();
}

Points: 0/3
// You created the class but never implemented the IUser interface. You need to use
// the implements keyword. Also there are no properties defined in the User class to use
// the this keyword. Also the greet function is defined incorrectly, it looks like you are 
// calling the greet function there instead of defining it. 

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Question 17:
What is the difference between public, private, and protected class members in TypeScript?

Answer:
a public variable can be changed anywhere (outside class), private can only be changed within a class, protected can be changed within derived classes.

Points: 2/2
// Good definitions! I'm assuming you mean inherited when you say derived. 

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Question 18:
Is the following valid TypeScript code? If not, explain the error and how to fix it.

Answer:
No, variable x cannot have color: "red" it has too many parameters.

Points: 0/2
// It was valid TypeScript code. If you remember the example, an object can be considered
// an interface shape if it has that interfaces properties, even if it has more properties.

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Question 19:
Which of the following allows adding new properties to an existing interface declaration across multiple files?

Answer:
Interface declaration merging

Points: 1/1

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Question 20:
Create an interface 'CartItem' with productId: number, quantity: number, and optional notes: string. Then write a function 'totalItems(items: CartItem[]): number' that returns the sum of quantities. Provide the code.

Answer:
Interface CartItem {
  productId: number;
  quantity: number;
  notes?: string;
  totalItems(items: CartItem[]): number
}

Points: 1/3
// You made an interface, but the totalItems function should be defined outside of
// the interface and should be fully implemented. 

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END OF QUIZ RESULTS --> 24/39 Points --> 62% 
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// Come see me if you have any questions about your grade.