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Lesson Content

Typed Functions in TypeScript

Functions in TypeScript can have typed parameters and return values, making them more predictable and easier to use.

Function Declarations

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

Arrow Functions

const multiply = (a: number, b: number): number => {
  return a * b;
};

// Shorthand
const divide = (a: number, b: number): number => a / b;

Optional Parameters

function greet(name: string, title?: string): string {
  if (title) {
    return `Hello, ${title} ${name}`;
  }
  return `Hello, ${name}`;
}

Default Parameters

function createUser(name: string, age: number = 18): object {
  return { name, age };
}

Rest Parameters

function sum(...numbers: number[]): number {
  return numbers.reduce((total, num) => total + num, 0);
}

Example Code

Practice writing typed functions

// Regular function
function greet(name: string): string {
  return `Hello, ${name}!`;
}

// Arrow function
const calculate = (x: number, y: number): number => x + y;

// With default parameter
function createMessage(text: string, prefix: string = "Info"): string {
  return `[${prefix}] ${text}`;
}

console.log(greet("TypeScript"));
console.log(calculate(5, 3));
console.log(createMessage("Learning TypeScript"));

Expected Output:

Hello, TypeScript!
8
[Info] Learning TypeScript

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