Summary - Objects

Write a user card by combining object types.

Summary - Objects

Object types let you model data precisely: shape defines properties, ? marks optional properties, and readonly marks immutable properties. Together they create safe and clear data structures.

let kullanici: {
  readonly id: number;
  ad: string;
  eposta?: string
} = { id: 1, ad: "Ali" };

These three features together create flexible but safe object types.

Exercise Write a user card

Declare a variable named kullanici with type { readonly id: number; ad: string; eposta?: string } and value { id: 1, ad: "Zeynep", eposta: "z@x.com" }. Print the value of kullanici.eposta with console.log.

Show example solution

let kullanici: { readonly id: number; ad: string; eposta?: string } = { id: 1, ad: "Zeynep", eposta: "z@x.com" };
console.log(kullanici.eposta);

Test yourself

Which type allows the value <code>{ ad: "Ali" }</code> but prevents reassigning <code>ad</code>?
- { readonly ad: string }
- { ad: string; tel?: string }
- { readonly id: number; ad: string }
- { ad?: string }
Show answer

{ readonly ad: string } — <code>{ readonly ad: string }</code> makes <code>ad</code> both required and immutable; the value <code>{ ad: "Ali" }</code> is valid and <code>ad</code> cannot be changed later.

Complete the optional property type

let kullanici: { readonly id: number; ad: string; eposta?: ____ } = { id: 1, ad: "Ali" };

Show answer

let kullanici: { readonly id: number; ad: string; eposta?: string } = { id: 1, ad: "Ali" };

Object concepts summary

{ ad: string }

Required property
tel?: string

Optional property
readonly id: number

Immutable property
Object type

Object shape

Next lesson: Function declaration

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