For example, when you want to work with JavaScript code which looks like:
ts
import greeter from "super-greeter";greeter(2);greeter("Hello world");
To handle both importing via UMD and modules:
ts
// Type definitions for [~THE LIBRARY NAME~] [~OPTIONAL VERSION NUMBER~]// Project: [~THE PROJECT NAME~]// Definitions by: [~YOUR NAME~] <[~A URL FOR YOU~]>/*~ This is the module template file for function modules.*~ You should rename it to index.d.ts and place it in a folder with the same name as the module.*~ For example, if you were writing a file for "super-greeter", this*~ file should be 'super-greeter/index.d.ts'*/// Note that ES6 modules cannot directly export class objects.// This file should be imported using the CommonJS-style:// import x = require('[~THE MODULE~]');//// Alternatively, if --allowSyntheticDefaultImports or// --esModuleInterop is turned on, this file can also be// imported as a default import:// import x from '[~THE MODULE~]';//// Refer to the TypeScript documentation at// https://www.typescriptlang.org/docs/handbook/modules.html#export--and-import--require// to understand common workarounds for this limitation of ES6 modules./*~ If this module is a UMD module that exposes a global variable 'myFuncLib' when*~ loaded outside a module loader environment, declare that global here.*~ Otherwise, delete this declaration.*/export as namespace myFuncLib;/*~ This declaration specifies that the function*~ is the exported object from the file*/export = Greeter;/*~ This example shows how to have multiple overloads for your function */declare function Greeter(name: string): Greeter.NamedReturnType;declare function Greeter(length: number): Greeter.LengthReturnType;/*~ If you want to expose types from your module as well, you can*~ place them in this block. Often you will want to describe the*~ shape of the return type of the function; that type should*~ be declared in here, as this example shows.*~*~ Note that if you decide to include this namespace, the module can be*~ incorrectly imported as a namespace object, unless*~ --esModuleInterop is turned on:*~ import * as x from '[~THE MODULE~]'; // WRONG! DO NOT DO THIS!*/declare namespace Greeter {export interface LengthReturnType {width: number;height: number;}export interface NamedReturnType {firstName: string;lastName: string;}/*~ If the module also has properties, declare them here. For example,*~ this declaration says that this code is legal:*~ import f = require('super-greeter');*~ console.log(f.defaultName);*/export const defaultName: string;export let defaultLength: number;}