What types exist only at compile time in Typescript - Mini Project: Build & Apply

What types exist only at compile time

📖 Scenario: Imagine you are learning TypeScript to write safer JavaScript code. You want to understand which types help you catch mistakes before running your program but do not exist when the program runs.

🎯 Goal: You will create some TypeScript types that exist only during compile time and see how they help check your code without affecting the final JavaScript output.

📋 What You'll Learn

Create a type alias called Fruit with exact string values 'apple', 'banana', and 'orange'.

Create an interface called Person with properties name (string) and age (number).

Create a variable favoriteFruit of type Fruit and assign it the value 'banana'.

Create a variable user of type Person with name 'Alice' and age 30.

Print the values of favoriteFruit and user.name.

💡 Why This Matters

🌍 Real World

TypeScript types help developers write safer code by catching mistakes early without slowing down the running program.

💼 Career

Understanding compile-time types is essential for frontend and backend developers using TypeScript to build reliable applications.

1

Create a type alias for fruits

Create a type alias called Fruit with the exact string values 'apple', 'banana', and 'orange'.

Typescript

// Your code here

Need a hint?

Use the type keyword and union of string literals.

2

Create an interface for a person

Create an interface called Person with properties name of type string and age of type number.

Typescript

type Fruit = 'apple' | 'banana' | 'orange';
// Your code here

Need a hint?

Use the interface keyword and define properties with types.

3

Create variables using the types

Create a variable called favoriteFruit of type Fruit and assign it the value 'banana'. Then create a variable called user of type Person with name set to 'Alice' and age set to 30.

Typescript

type Fruit = 'apple' | 'banana' | 'orange';

interface Person {
    name: string;
    age: number;
}

// Your code here

Need a hint?

Use const to declare variables with the types you created.

4

Print the variable values

Write two console.log statements to print the values of favoriteFruit and user.name.

Typescript

type Fruit = 'apple' | 'banana' | 'orange';

interface Person {
    name: string;
    age: number;
}

const favoriteFruit: Fruit = 'banana';
const user: Person = { name: 'Alice', age: 30 };

// Your code here

Need a hint?

Use console.log(favoriteFruit) and console.log(user.name).