Exploring TypeScript Module Importation and WebPack Integration

Struggling with WebPack's injection of imported dependencies for a TypeScript project. The first challenge is getting TypeScript to recognize the imported module.

In the header.ts file, there is a declaration of a module nested under vi.input, exporting a VIInputDirective class. In the main.ts file, attempts are made to import this exported VIInputDirective class from header.ts, but TypeScript fails to recognize it.

header.ts

module vi.input.header {
  import IDirective = angular.IDirective;

  export class VIInputDirective implements IDirective {
    ...
  }
}

main.ts

import {VIInputDirective} from "./header.ts"; // Unable to import; Resolve issue
VIInputDirective.whatever(); // Not functional

material.dt.s

declare module vi.input {
  ...
}

Substituting

import VIMHeaderDirective = vi.input.header.VIInputDirective;
in the main.ts file resolves the issue, but triggers an error during webpack transpile/injection:

VM1469:1Uncaught ReferenceError: vi is not defined

Several approaches were tested like exporting the vi.input.header module directly, using reference syntax to include the file, and removing the nesting of modules - only to find that the latter solution works. However, the preference is to maintain the structure within a nested module.

Answer №1

Your code structure does not utilize modules. Instead, it relies on the global namespace and subnamespaces of the global namespace to organize the program, following what is known as the revealing module pattern.

It's worth noting that TypeScript used to refer to this pattern as "Internal Modules," but now discourages the use of the module x {} syntax in favor of the namespace keyword to reduce confusion.

JavaScript loaders like Webpack work with modules, referred to by TypeScript as "external modules." The constructs you are using are not directly related to true modules.

  1. Any top level, non-exported module/namespace declarations do not strictly constitute module usage.

    namespace vi.input.header { ... }
    

    This should instead be written as:

    namespace vi.input.header { ... }
    

    The emission result has always involved mutating the global scope, commonly used by libraries. These "internal modules" allow multiple files to contribute to their contents, regardless of their nested structure or assignment patterns.

  2. import assignments referencing namespace members don't qualify as top-level import declarations, deviating from true module systems like AMD, CommonJS, etc.

While your code may include some TypeScript-specific features like

import name = qualified.global.name
, they are distinct from genuine modules.

However, namespaces within external modules can be elegantly utilized for internal code organization but have unique semantics compared to standalone namespaces.

It's crucial to distinguish between these different approaches when structuring your application. For instance, if utilizing a bundling tool like Webpack, adhere to proper module usage throughout your codebase.

In conclusion, the key lies in understanding the differences between module structures and organizing your code accordingly for efficient development and maintenance.

Answer №2

If you are seeking namespaces and not modules, take a look at the following code snippet.

header.ts

export namespace vi.input.header {
  export class VIInputDirective {

  }
}

main.ts

import { vi } from "./header.ts"; 
var example = new vi.input.header.VIInputDirective();

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