- Parameter and return types:
function add(a: number, b: number): number - Optional parameter:
title?: string - Default value:
greeting = "Hello" - Rest parameters:
...nums: number[] - Function type:
type Op = (a: number, b: number) => number;
TypeScript Functions
Typed parameters, return types and optional parameters.
✍️ 3 exercises + code challenge in this lessonKey Takeaways: TypeScript Functions
Mastering TypeScript Functions helps you write clean and reliable TypeScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
TypeScript Functions Code Example
TypeScriptfunction sum(...nums: number[]): number {
return nums.reduce((a, b) => a + b, 0);
}
function greet(name: string, greeting = "Hello", title?: string): string {
return `${greeting}, ${title ? title + " " : ""}${name}`;
}
type Op = (a: number, b: number) => number;
const multiply: Op = (a, b) => a * b;
console.log(sum(1, 2, 3));
console.log(greet("Khan", "Salam", "Mr."));
console.log(multiply(6, 7));Output
6 Salam, Mr. Khan 42
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TypeScript Functions Practice Exercises
Check what you learned in “TypeScript Functions”.
/ 3 solved
Fill in the blank
Declare the return type.
function add(a: number, b: number) { return a + b; }
✓ Correct!
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Multiple choice
How do you mark a parameter as optional?
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Code challenge
Write greet(name: string, greeting = "Hello") returning "greeting, name!" and log greet("Usman").
Write the code in the live editor. Your answer is checked automatically.
✓ Solved
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