Functions – Parameter & Return Types

Function Signatures

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

The compiler checks both parameter and return types.

Optional Parameters (?)

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

Default Parameters

function multiply(a: number, b: number = 2): number {
  return a * b;
}

Rest Parameters (...)

function sum(...values: number[]): number {
  return values.reduce((a, b) => a + b, 0);
}

Void vs. Undefined

function log(msg: string): void {
  console.log(msg);
  // implicit return of undefined
}