Function Signatures

Function Signatures

A function signature describes what a function looks like — its parameter types and return type — without implementing it.

Basic Function Signature

let greet: (name: string, greeting: string) => void;

greet = (name: string, greeting: string) => {
    console.log(`${greeting}, ${name}`);
};

Signature with Return Type

let calc: (a: number, b: number, action: string) => number;

calc = (a: number, b: number, action: string) => {
    if (action === "add") return a + b;
    if (action === "subtract") return a - b;
    return 0;
};

Signatures with Objects

type Person = { name: string; age: number };

let logDetails: (obj: Person) => void;

logDetails = (ninja: Person) => {
    console.log(`${ninja.name} is ${ninja.age}`);
};

Using Type Aliases for Signatures

type MathFunc = (a: number, b: number) => number;

const add: MathFunc = (a, b) => a + b;
const subtract: MathFunc = (a, b) => a - b;

Key Takeaways

• Function signatures define parameter and return types
• The implementation must match the signature
• Use type aliases for reusable function signatures
• Great for callbacks and function parameters