Namespace declaration in Typescript - Mini Project: Build & Apply

Namespace Declaration in TypeScript

📖 Scenario: Imagine you are organizing a small library of books. You want to group related functions and variables under a common name to keep things tidy and avoid name clashes.

🎯 Goal: You will create a Library namespace that contains a list of books and a function to display the books.

📋 What You'll Learn

Create a namespace called Library

Inside Library, create a variable books which is an array of strings

Inside Library, create a function showBooks that prints each book name

Call the showBooks function outside the namespace to display the books

💡 Why This Matters

🌍 Real World

Namespaces help organize code in large projects by grouping related code together and avoiding name conflicts.

💼 Career

Understanding namespaces is important for working on TypeScript projects, especially when collaborating with others or managing big codebases.

1

Create the Library namespace with a books array

Create a namespace called Library and inside it create a variable called books which is an array containing these exact strings: 'The Hobbit', '1984', 'Brave New World'.

Typescript

namespace Library {
  // Create the books array here
  // Your code here
}

Hint

Use namespace Library { } to start. Inside, declare export const books as an array of strings.

2

Add the showBooks function inside Library

Inside the Library namespace, add a function called showBooks that loops over the books array and prints each book name using console.log.

Typescript

namespace Library {
  export const books: string[] = ['The Hobbit', '1984', 'Brave New World'];

  // Add the showBooks function here
  // Your code here
}

Hint

Define export function showBooks(). Use a for...of loop to print each book.

3

Call the showBooks function outside the namespace

Outside the Library namespace, call the showBooks function using the namespace prefix to display the list of books.

Typescript

namespace Library {
  export const books: string[] = ['The Hobbit', '1984', 'Brave New World'];

  export function showBooks(): void {
    for (const book of books) {
      console.log(book);
    }
  }
}

// Call the showBooks function here
// Your code here

Hint

Use Library.showBooks() to call the function outside the namespace.

4

Display the list of books using the namespace function

Run the program to display the list of books. The output should show each book name on its own line.

Typescript

namespace Library {
  export const books: string[] = ['The Hobbit', '1984', 'Brave New World'];

  export function showBooks(): void {
    for (const book of books) {
      console.log(book);
    }
  }
}

Library.showBooks();

// Observe the output above

Hint

Check the console output. You should see each book name printed on its own line.

Practice

1. What is the main purpose of a namespace in TypeScript?

easy

A. To import external libraries

B. To create a new type of variable

C. To define a function that runs automatically

D. To group related code under one name and avoid name clashes

Solution

1. Step 1: Understand what namespaces do

   Namespaces group related code together to keep it organized.

2. Step 2: Recognize the benefit of namespaces

   They help avoid name clashes by keeping code under one name.

3. Final Answer:

   To group related code under one name and avoid name clashes -> Option D

4. Quick Check:

   Namespaces = Group code + avoid clashes [OK]

Hint: Namespaces group code to avoid name conflicts [OK]

Common Mistakes:

• Thinking namespaces create new variable types
• Confusing namespaces with functions
• Assuming namespaces import libraries

2. Which of the following is the correct syntax to declare a namespace named Utils in TypeScript?

easy

A. namespace Utils { }

B. module Utils { }

C. package Utils { }

D. namespace = Utils { }

Solution

1. Step 1: Recall the correct keyword for namespaces

   TypeScript uses the keyword namespace to declare namespaces.

2. Step 2: Check the syntax format

   The correct syntax is namespace Name { }, so namespace Utils { } is correct.

3. Final Answer:

   namespace Utils { } -> Option A

4. Quick Check:

   Namespace syntax = namespace Name { } [OK]

Hint: Use 'namespace Name { }' to declare namespaces [OK]

Common Mistakes:

• Using 'module' instead of 'namespace'
• Adding '=' sign in declaration
• Using 'package' keyword which is invalid

3. What will be the output of the following TypeScript code?

namespace MathOps {
  export function add(a: number, b: number) {
    return a + b;
  }
}

console.log(MathOps.add(3, 4));

medium

A. undefined

B. 7

C. Error: add is not defined

D. NaN

Solution

1. Step 1: Understand the namespace and export usage

   The function add is inside namespace MathOps and is exported, so it can be accessed outside.

2. Step 2: Evaluate the function call

   Calling MathOps.add(3, 4) returns 3 + 4 = 7.

3. Final Answer:

   7 -> Option B

4. Quick Check:

   Exported function call returns sum 7 [OK]

Hint: Exported namespace members are accessible outside [OK]

Common Mistakes:

• Forgetting to export the function
• Trying to call function without namespace prefix
• Expecting runtime errors due to namespace

4. Identify the error in this TypeScript namespace code:

namespace Data {
  function getData() {
    return "info";
  }
}

console.log(Data.getData());

medium

A. Function getData is not exported, so it cannot be accessed outside

B. Namespace name Data is invalid

C. Syntax error in namespace declaration

D. Console.log is misspelled

Solution

1. Step 1: Check function accessibility inside namespace

   The function getData is declared but not exported, so it's private to the namespace.

2. Step 2: Understand why console.log(Data.getData()) fails

   Since getData is not exported, it cannot be accessed outside the namespace, causing an error.

3. Final Answer:

   Function getData is not exported, so it cannot be accessed outside -> Option A

4. Quick Check:

   Export missing = access error [OK]

Hint: Export functions to access them outside namespaces [OK]

Common Mistakes:

• Assuming all namespace members are public by default
• Thinking namespace name is invalid
• Ignoring export keyword importance

5. Given two namespaces below, what is the correct way to call the log function from Logger inside App?

namespace Logger {
  export function log(message: string) {
    console.log("LOG: " + message);
  }
}

namespace App {
  export function run() {
    // Call Logger.log here
  }
}

App.run();

hard

A. log("App started");

B. App.Logger.log("App started");

C. Logger.log("App started");

D. Logger::log("App started");

Solution

1. Step 1: Understand namespace access rules

   Namespaces are accessed by their name followed by dot and member name, so Logger.log is correct.

2. Step 2: Check the options for calling the function

   Only Logger.log("App started") correctly calls the exported function from the Logger namespace.

3. Final Answer:

   Logger.log("App started"); -> Option C

4. Quick Check:

   Namespace function call = NamespaceName.member [OK]

Hint: Call namespace functions with NamespaceName.function() [OK]

Common Mistakes:

• Calling function without namespace prefix
• Using invalid syntax like '::'
• Assuming nested namespaces auto-import members