Ambient declarations in Typescript - Mini Project: Build & Apply

Using Ambient Declarations in TypeScript

📖 Scenario: You are building a TypeScript project that uses a JavaScript library called mathLib. This library is loaded separately and provides a function to calculate the square of a number. Since TypeScript does not know about this library by default, you need to tell TypeScript about it using ambient declarations.

🎯 Goal: Learn how to create an ambient declaration for an external JavaScript function and use it safely in TypeScript.

📋 What You'll Learn

Create an ambient declaration for the external function square.

Use the declared square function in TypeScript code.

Print the result of calling square with a number.

💡 Why This Matters

🌍 Real World

Ambient declarations help TypeScript understand code from external JavaScript libraries that do not have type information.

💼 Career

Many real-world projects use third-party JavaScript libraries. Knowing how to write ambient declarations lets you safely use these libraries in TypeScript.

1

Create an ambient declaration for the square function

Write an ambient declaration for a function called square that takes a number and returns a number. Use the declare keyword.

Typescript

// Declare the ambient function 'square'
declare function square(x: number): number;

Need a hint?

Use declare function followed by the function name and its type signature.

2

Create a variable to hold a number to square

Create a variable called num and set it to the number 5.

Typescript

declare function square(x: number): number;

// Create a variable 'num' and set it to 5
let num = 5;

Need a hint?

Use let num = 5; to create the variable.

3

Call the ambient square function with num

Create a variable called result and set it to the value returned by calling square(num).

Typescript

declare function square(x: number): number;

let num = 5;

// Call square(num) and store in 'result'
let result = square(num);

Need a hint?

Use let result = square(num); to call the function and store the result.

4

Print the result to the console

Write a console.log statement to print the value of result.

Typescript

declare function square(x: number): number;

let num = 5;

let result = square(num);

// Print the result
console.log(result);

Need a hint?

Use console.log(result); to display the output.