Looking for help with importing modules/namespaces in TypeScript?

I am currently using TypeScript 2.1.5 in conjunction with Visual Studio 2015. The project has been set up to utilize the "ES 2015" module system and ECMAScript 6.

My current challenge involves implementing the Angular Local Storage module, as outlined by DefinitelyTyped:

declare module 'angular' {
    export namespace local.storage {
        interface ILocalStorageService { 
        }
    }
}

Therefore, in one of my services, I aim to import this interface for practical use:

module Foooooo.Services {
    export class FooService {
        constructor(private localStorageService: local.storage.ILocalStorageService) {

        }
    }
}

Despite extensive research and studying the documentation thoroughly, I have tried multiple methods without success:

import local from "angular";                           // unsuccessful attempt
import * as ang from "angular";                        // causing resolution issues with other interfaces
import { local } from "angular";                       // compilation failure
import { ILocalStorageService } from "angular";        // unresolved interfaces
import { local.ILocalStorageService } from "angular";  // not working
import ILocalStorageService = require("angular");      // unsurmountable error message regarding compatibility with ECMAScript 6 or newer

How can I achieve a successful import in this scenario?

Answer №1

To view my solution, click on this link. Ensure to run npm install followed by npm run build to verify that it compiles correctly.

There are two methods to tackle the issue at hand. You can opt for modules (formerly referred to as "external modules") or namespaces (previously known as "internal modules"). The repository contains 2 corresponding *.ts files for each approach.

In module.ts, you explicitly declare the import of the 2 dependencies: angular and angular-local-storage. The import of angular-local-storage serves as a "side effect" because it enhances angular without exporting any additional elements. Following import 'angular-local-storage', importedAngular (the variable containing whatever is exported by angular) now acknowledges the supplementary properties/methods introduced by angular-local-storage.

As for namespace.ts, there exists only a minor deviation from the sample highlighted in your initial query. Given that angular exports a global type angular (for application with script tags), one can simply utilize that type. This global type has already been "patched" by angular-local-storage since within "internal modules"/namespaces under a "project" (any directory incorporating a tsconfig.json file), TypeScript will encompass all d.ts files during compilation, where one of those d.ts files (particularly within @types/angular-local-storage) enriches the angular global type. Should you delete the @types/angular-local-storage from within node_modules, compilation would fail for namespace.ts.

It is advisable to favor the module approach over the namespace strategy due to many packages lacking the UMD global type, resulting in the failure of the latter method.

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