Modules

The concept of modules first appeared in the ECMAScript 2015 standard. Modules allow you to split a complex application into separate files, each of which contains strictly defined functionality, and then, using import, to put them together. Variables, classes, functions declared in a module are not available from outside this module, unless they are exported using the export command. And in order to use the exported parts in another module, you need to import them using the import command.

Export

Any declaration can be exported using the export keyword.

Playground Link

// Экспорт переменной
let fruit: string = 'banana',
  device: string = 'smartphone',
  bool: boolean = true
export { fruit, device, bool as isBool }

// Экспорт константы
export const e = 2.7182818284590452353602874713526625

// Экспорт функции
export function sum(x, y: number): number {
  return x + y
}

// Экспорт интерфейса
export interface Fruit {
  name: string;
  sweetness: number;
  bones: boolean;
}

// Экспорт класса
export class Animal {
  move(distanceInMeters: number = 0) {
    console.log(`Animal moved ${distanceInMeters}m.`)
  }
}

// Экспорт всего сразу
export { fruit, e, sum, Fruit, Animal }

Default export

Using the keyword default you can export by default.

Playground Link

export default class User {
    constructor(public name) {}
}

Import

You can connect the exported functionality of the module using the keyword import.

Playground Link

// Импорт пример
import { A, B } from './scripts'

// Импорт для экспорта по умолчанию
import User from './users'

// Импорт с другим именем
import { A as a, B } from './scripts'

// Импорт всех модулей
import * as scripts from './scripts'
let a = scripts.A

Re-export

In a module, you can re-export the functionality of some other module using the export .. from construction. In this case, no import is performed locally and the variable is not created.

Playground Link

export { B as b } from './scripts'

Questions

Now we are ready to study TypeScript with you, but in order to understand how much you learned this lesson, take the test in the mobile application in our school on this topic.