04. Namespaces and Modules

Namespaces

Definition

• Namespaces are used to logically group functionalities
• Previously referred to as internal modules in TypeScript
• Defined with namespace keyword
• Namespaces may include functions, classes, interfaces, and variables

Access

• The elements of the namespace that must be accessed from the outside must be marked with export keyword
• In order to access namespaces from different files we must use the reference syntax
  /// <reference path = "file.ts" />

Multiple Files Namespaces

• In order to access namespaces from different files we must use the reference syntax /// <reference path = "file.ts" />
• In order to compile the file we must

Compile the ts file - tsc fileName.ts Use the outFile - tsc --outFile fileName.js fileName.ts Compile the js file - node fileName

Aliases

• Used to simplify the work with namespaces
• Used with import keyword
• Often used as nested namespaces

Modules

Definition

• Modules are executed in their own scope, not the global
• A set of functions to be included in applications
• Resolve name collisions
• In order to be accessed from the outside they need to be marked with an export keyword

Access

• To consume a function, class, interface, or variable exported from another module we must use an import form

import { name } from "./location" - import specific element import * as variable from "./location"; - imports the entire module in single variable

Export Statements

• There are three ways to use export statements:

A: export function numberValidation(num: number): number {…} B: export { numberValidation }; C: export { numberValidation as isValidNum }; //isValidNum is alias D: export default function stringValidations(string: string): string {…}

• In cases A and B there is no difference rather than syntax
• There might be only one export default in a file

Import Statements and File Compilation

• In order to compile the file we must

Compile the ts file - tsc fileName.ts Use the outFile - tsc --module commonjs fileName.ts Compile the js file - node fileName

Namespaces vs Modules

• Namespaces: Global containers for code organization.
• Enclosed using namespace keyword.
• Can be split across multiple files but combined during compilation.
• Can contain variables, interfaces, functions, classes, etc. Modularize code into separate files.
• Enclosed using export and import keywords.
• Are more file-based and can be loaded asynchronously.
• Can contain variables, functions, classes, etc., but not directly at the root level.