API response type

Write the API response type with interface.

What is an API response type?

Data coming from a weather API usually has a fixed structure. You define this structure with an interface. Sometimes the API may omit some fields; in that case you mark those fields as optional. This way both real API data and incomplete responses are handled type-safely.

interface ApiResponse {
  city: string;
  temperature: number;
  humidity?: number;
}

Required and optional fields

Fields always present in an API response are required and declared with :. Fields that may sometimes be missing are made optional with ?. For example, city always arrives but humidity may be absent in some responses. This separation preserves data consistency.

interface ApiResponse {
  city: string;        // required
  temperature: number; // required
  humidity?: number;   // optional
}

Exercise API response interface

Define an ApiYanit interface: sehir: string and sicaklik: number required, nem?: number optional. Create an ApiYanit object named y with only sehir: "İzmir" and sicaklik: 25. Print y.sehir with console.log.

Show example solution

interface ApiYanit {
  sehir: string;
  sicaklik: number;
  nem?: number;
}
const y: ApiYanit = { sehir: "İzmir", sicaklik: 25 };
console.log(y.sehir);

Test yourself

How is a field that may sometimes be absent in an API response marked?
- With void
- With the const keyword
- With readonly
- Made optional with ?
Show answer

Made optional with ? — Optional fields are marked with ?; if the field is absent it is accepted as undefined and causes no compile error.

Optional field marker

interface ApiYanit {
  sehir: string;
  nem____: number;
}

Show answer

interface ApiYanit {
  sehir: string;
  nem?: number;
}

API response concepts

interface

Structure definition
?

Optional field marker
nem

Humidity field
yanit

API return data

Next lesson: Data transform

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