Summary - Functions

Write a store calculation function with types.

Summary - Functions

Functions combine type annotations, optional and default parameters, rest parameters, and overloading to create powerful and flexible definitions. Choosing the right features improves both type safety and usability.

function hesapla(fiyat: number, oran: number = 10): number {
  return fiyat - (fiyat * oran) / 100;
}

These features together enable writing safe and flexible functions.

Exercise Store calculation function

Define a function named indirimli with fiyat: number and oran: number = 10 parameters and return type number. The function should return fiyat - (fiyat * oran) / 100. Print the result of calling indirimli(200) with console.log.

Show example solution

function indirimli(fiyat: number, oran: number = 10): number {
    return fiyat - (fiyat * oran) / 100;
}
console.log(indirimli(200));

Test yourself

Which feature lets a function accept any number of arguments?
- Default parameters
- Rest parameters
- Return type annotation
- Optional parameters
Show answer

Rest parameters — A rest parameter (<code>...args</code>) collects a variable number of arguments into a single array; optional and default parameters only provide skippable parameters.

Add the default parameter value

function indirim(fiyat: number, oran = ____): number { return fiyat - (fiyat * oran) / 100; }

Show answer

function indirim(fiyat: number, oran = 10): number { return fiyat - (fiyat * oran) / 100; }

Function concepts summary

function f(a: number): number

Typed function
oran?: number

Optional parameter
...sayilar: number[]

Rest parameter
oran: number = 10

Default parameter

Next lesson: Arrow syntax

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