What is best practice: Using Typescript types on Incoming JSON data in Angular, or not

Question

I do a REST request and get back JSON. Assume recent versions of Angular/TS.

What is 'best practice' here:

1. Do nothing with the received JSON in terms of Types and just treat it as 'any' and put its data in the destination object(s).

const localTypedObj: UserData;
localTypedObj.userId = dataFromRestReq.userId

2. Give the incoming JSON a type/name and then use that:

type NewTypeName = typeof dataFromRestReq;
const newlyTypedData: NewTypeName = dataFromRestReq;

localTypeObj.userId = newlyTypedData.userId; // Here the editor knows that userId is a thing!

3. Create a Type/Interface to then apply to the incoming data:

interface NewTypeName {
userId: string;
}
// elsewhere...
let newlyTypedData = <NewTypeName>dataFromRestReq;

4. Other?

Am I restricting things too much here, if an extra item is added to the JSON by back-end folks, will front-end crash if the type is expecting a certain format?

Answer 1

It depends on what you do with the data.

If you only read it, so you can use a interface. It helps to avoid typos and makes all better readable. Sample:

export enum UserRole {
  admin = 10,
  guest = 5,
}

export interface UserLogin {
  userName: string;
  role: UserRole;
  token: string;
}

...

this.httpClient.get<UserLogin>(......).subscribe(data => {
  data.[no typos and a clean way] // Save to localStorage and so on
})

If you work with the data; so you wanna manipulate it as example, it is a good way to use a class:

export class UserLogin {
  public userName: string;
  public role: UserRole;
  public token: string;

  constructor() { }

  sayHello() {
    return "Hello " + userName + "!";
  }
}

...

this.httpClient.get<UserLogin>(......).subscribe(data => {
  const newUser = Object.assign(new UserLogin(), data)
  this.users.push(newUser); // Or do anything
  newUser.sayHello();
})

Many ways are ok. So nothing is wrong to use a class, a interface a enum or anything else. It depends only on what you wanna do with the data.

I hope it makes it more clear for you.