Optional properties

Learn optional properties with ?.

Optional properties

Some properties may not always be present. You make them optional by placing ? after the property name. An optional property may or may not be present in the object.

let kisi: { ad: string; tel?: string } = {
  ad: "Ali"
};  // tel missing, valid

With ? a property becomes optional and can be omitted.

Accessing optional properties

When you access an optional property, its value may be undefined if not set. It is safe to check whether it is defined before using it.

let kisi: { ad: string; tel?: string } = {
  ad: "Ali"
};
console.log(kisi.tel);  // undefined

Optional properties may have the value undefined.

Exercise Object with an optional property

Declare a variable named kisi with type { ad: string; tel?: string } and value { ad: "Can", tel: "555" }. Print the value of kisi.tel with console.log.

Show example solution

let kisi: { ad: string; tel?: string } = { ad: "Can", tel: "555" };
console.log(kisi.tel);

Test yourself

What does <code>tel?: string</code> mean?
- tel property cannot be assigned
- tel property is optional and may be absent
- tel property is of type number
- tel property must be a string
Show answer

tel property is optional and may be absent — The <code>?</code> mark makes a property optional; <code>tel?: string</code> means the <code>tel</code> property may or may not be present.

Make the property optional

let urun: { ad: string; indirim____: number } = { ad: "kalem" };

Show answer

let urun: { ad: string; indirim?: number } = { ad: "kalem" };

Optional property concepts

tel?: string

Optional string property
tel: string

Required string property
? (özellik adından sonra)

Makes a property optional
Optional property

Property may be absent

Next lesson: Readonly properties

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