How to declare and import typescript interfaces in a separate file

Question

I want to define several interfaces in their own file in my typescript-based project, from which I\'ll implement classes for production as well as mocks for testing. However

Answer 1

Export only a few interfaces

Without spreading multiple exports, you can group them in one single export {} block (in this case, no file default type should be declared):

// interfaces.ts
interface IWords {
  [key: string]: string; 
}

interface INumbers {
  [key: string]: number; 
}

interface IBooleans {
  [key: string]: boolean; 
}

interface IValues {
  [key: string]: string | number; 
}

interface IStructures {
  [key: string]: INumbers | IBooleans | IValues;
}

export {
  // not exporting IWords | INumbers
  IBooleans,
  IValues,
  IStructures,
}

Import example

import { IBooleans, IValues, IStructures } from 'interfaces';

const flags: IBooleans = { read: true, write: false, delete: false };

const userFile: IValues = { user: 1, username: 'One', file: 'types.txt' };

const userContext: IStructure = {
  file: userFile,
  permissions: flags,
  counts: { views: 3, writes: 1 } // => INumbers (lint: try to remove IValues from IStructures)
};