CODEWITHSUNDEEP
typescriptangular
Supamiu
Supamiu

Reputation: 8731

Cast not casting

I made a simple Http call:

http.get('/test/data/user.json').
    map(res => <User> res.json()).
    subscribe(user => {
        console.log(typeof user);
        console.log(user);
        console.log(user.getName());
});

with the following data in user.json:

{
    "name":"Robert"
}

and the following User class:

export class User{
    name:string;
    lastName:string;
    getName():string{
        return this.name;
    }
}

Problem is the result I get in console:

console.log(typeof user);

object

console.log(user);

Object {name: "Robert"}

console.log(user.getName());

Uncaught TypeError: user.getName is not a function

Problem

Problem here is that my object is an object, not a User, so it does not have all properties, and it has no methods.

Also tried with Promise-based call and user.json() as User instead of <User> res.json()

EDIT: not similar to casting to an interface since interface doesn't have its own behaviour.

Upvotes: 4

Views: 1523

Answers (1)

Thierry Templier
Thierry Templier

Reputation: 202326

If you want to use the getName method, you need to instantiate an new User object when mapping the response body:

http.get('/test/data/user.json').
  map(res => {
    let body = res.json();
    return new User(body.name, body.lastName);
  })
  subscribe(user => {
    console.log(typeof user);
    console.log(user);
    console.log(user.getName());
  });

The User class would be adapted like below:

export class User{
  constructor(private name:string, private lastName:string) {}

  getName():string{
    return this.name;
  }
}

Casting an object won't add method to an existing object. The json method of the response will simply parse the response body using JSON.parse and return a raw object.

See this plunkr: https://plnkr.co/edit/7lKHvArpayrMAzm5Xgk1?p=preview.

Upvotes: 3

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