TypeScript Interface Undefined

Question

I have this:

  public getFriends() : IUser[] {
    let friends: IUser[];
    friends[0].Id = "test";
    friends[0].Email = "asdasd";

    return friends;
  }

Could sound stupid, but why am I getting friends[0] undefined? What am I supposed to do if I don't have a class of type User in this case.

Only the type is declared for the field but not initialized. e.g. let friends: IUser[] = []. — Shane
– Shane, Commented Aug 20, 2017 at 19:35
At no point are you creating the array, and much less an object in that array. — deceze
– deceze ♦, Commented Aug 20, 2017 at 19:38

acdcjunior · Accepted Answer · 2017-08-20 19:40:48Z

In this statement:

let friends: IUser[];

You are declaring friends and its type IUser[], you aren't initializing it yet, so friends's value is undefined at this point.

So, the first step is to initialize it:

let friends: IUser[] = [];

Now it is an array, you have to push some content into it. First you have to create a IUser:

// this is one (likely) way of creating a IUser instance, there may be others
let friend: IUser = {Id: "test", Email: "asdasd"};

And then add it to the array:

friends.push(friend);

So your final code would be:

public getFriends() : IUser[] {
    let friends: IUser[] = [];

    let friend: IUser = {Id: "test", Email: "asdasd"};
    friends.push(friend);

    return friends;
}

Collectives™ on Stack Overflow

TypeScript Interface Undefined

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related