How to declare iterable object of another interface type?

Question

So, here I'm trying to make interface type of Object which will contain only specific interfaces in it. For example:

export interface IUser {
  name: string;
  last: string;
};

export interface IRoom {
  users: Object<IUser>; // this is wrong.
}

I'm expecting, that users will be something like:

Users: {
  'user_id_goes_here': {
    name: 'John',
    last: 'Doe'
  },
  'user_id_goes_here': {
    name: 'Albert',
    last: 'Einstein'
  },
  ...
}

Is there any way to define interface member type like this?

Daniel Rosenwasser · Accepted Answer · 2016-11-07 03:48:25Z

3

I think you want something like this:

export interface Room {
    users: UserMap;
}

export interface UserMap {
    [userId: string]: User;
}

export interface User {
    name: string;
    last: string;
}

That [userId: string]: IUser; is what's called a string index signature. It means that whenever you use a string to index into a UserMap, you will get an IUser.

edited Nov 7, 2016 at 3:48

answered Nov 6, 2016 at 2:38

Daniel Rosenwasser

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3 Comments

Nika Over a year ago

Thanks for the answer! I was not sure what I should search in google though. Now I remember it's a map type.

Daniel Rosenwasser Over a year ago

Sure, index signatures are meant to model map-like objects in JavaScript, but it's not obvious what they'd be called. Hopefully someone searching finds this answer. As a heads up, if all you're using these for is the type, you can use an interface declaration instead of a class (since interfaces don't have any emit).

Nika Over a year ago

You're right. I forgot to mention the interface, it was quickly written example without much thinking and was tired. Thanks for advise! P.S edited the question, replaced class with interface.

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