This interface describes my answers array (IActivityAnswer[]).

export interface IActivityAnswer {
  createdAt: string;
  id: string;
  questionId: string;
  score: number;
  summary: string;
  title: string;
  mentCount?: number;
}

Some users won't have any answers (so they will have an empty array). How do I define a type for empty array. I want to acplish this without using type any.

This interface describes my answers array (IActivityAnswer[]).

export interface IActivityAnswer {
  createdAt: string;
  id: string;
  questionId: string;
  score: number;
  summary: string;
  title: string;
  mentCount?: number;
}

Some users won't have any answers (so they will have an empty array). How do I define a type for empty array. I want to acplish this without using type any.

• javascript
• reactjs
• typescript

• 1 What type would you like the array to have? How do you plan on using it? – Tom Fenech Commented Sep 14, 2018 at 15:16
• 3 If you're not going to store anything in it, why have that array anyway? – Andreas Commented Sep 14, 2018 at 15:17
• What's the sense of this question? – Jacopo Sciampi Commented Sep 14, 2018 at 15:23
• @TomFenech This interface describes the populated array: export interface IActivityAnswer { createdAt: string; id: string; questionId: string; score: number; summary: string; title: string; mentCount?: number; } I make an api call to get data. While the api call is pending the array is empty. – Jen Commented Sep 14, 2018 at 15:37
• 1 Wele to Stack Overflow! For best results, please review the documentation on how to ask a good question and what constitutes a minimal reproducible example. – jcalz Commented Sep 14, 2018 at 15:42

2 Answers 2

As of TypeScript 3.0, you can use the empty tuple type, written [].

const empty: [] = [];

However, even without this feature, I don't understand why you would need to use any since you could write something like

const empty = <never[] & {length: 0}>[];

The empty tuple type [] should be preferred as it provides more robust checking and better error messages when misused.

You can specify IActivityAnswer[] and the type would be defined as the following:

An array containing IActivityAnswer objects, or an array not containing IActivityAnswer objects, i.e. an empty array.