Example of TypeScript Ambient Namespace Usage

Question

Example of TypeScript Ambient Namespace Usage

The Namespaces chapter provides an example involving D3.d.ts that I find puzzling.
Here is the complete example:

declare namespace D3 {
    export interface Selectors {
        select: {
            (selector: string): Selection;
            (element: EventTarget): Selection;
        };
    }

    export interface Event {
        x: number;
        y: number;
    }

    export interface Base extends Selectors {
        event: Event;
    }
}

declare var d3: D3.Base;

My main confusion lies in how to actually incorporate D3.d.ts into my modules or typescript scripts. Can you provide me with some brief examples?

EDIT
Please disregard the specific use of D3; it could be any other library like B3, G3, X7... I am solely interested in understanding how to utilize the example provided in my typescript modules and scripts.

EDIT2 What mainly perplexes me is the usage of declare namespace ... in the above example instead of simply namespace D3 (similar to how namespace Validation is used). Additionally, what is the purpose of and how do I utilize declare var d3: D3.Base;?

typescript namespaces ambient

Answer 1

Answer №1

These statements establish global variables that are not derived from imports but may be set on the window by a <script>. If you want to access these variables directly (without imports), you can always create a reference like this:

/// <reference path="../types/D3.d.ts" />
d3.select("div"); // No import!

If the declaration file is located in an @types directory, it should be included without a specific reference.

The use of declare in the namespace is necessary because this is a declaration file: It must either export the namespace (which applies only to modules) or declare it to make these types accessible.

Answer 2

These statements establish global variables that are not derived from imports but may be set on the window by a <script>. If you want to access these variables directly (without imports), you can always create a reference like this:

/// <reference path="../types/D3.d.ts" />
d3.select("div"); // No import!

If the declaration file is located in an @types directory, it should be included without a specific reference.

The use of declare in the namespace is necessary because this is a declaration file: It must either export the namespace (which applies only to modules) or declare it to make these types accessible.

Answer 3

Answer №2

My understanding of TypeScript is that the example code provided does not actually generate or modify any JavaScript output. Instead, it consists of declarations that serve to assist in error checking by IntelliSense and the TypeScript compiler, without directly impacting the code itself. These declarations are meant for an "ambient" declaration file, which provides TypeScript definitions for regular JavaScript libraries, enabling TypeScript and IntelliSense to work with them as if they were native TypeScript files rather than plain JavaScript. When TypeScript encounters something without a corresponding declaration, it typically treats it as an "any" type.

For the mentioned library, it is recommended to utilize the existing type library (npm install --save-dev @types/d3). After installing both the library (npm install --save d3) and its types @types/d3, using import * as d3 from 'd3' in a .ts file (in Angular 5; other setups may vary) successfully brings in the object and type information. The contents of the types file will differ significantly from those in the TypeScript documentation example, but they all consist of declarations rather than executable code.

Regarding the edits

The file in question is not a primary TypeScript file but a declarations file outlining the "TypeScript shape" of a standard JavaScript library - essentially guiding how the TypeScript compiler and IntelliSense should interpret the structure of the JavaScript code if it were written in TypeScript. Despite appearances, the choice of naming it D3 was intentional. The .d.ts file aims to offer TypeScript metadata for a library like D3 (https://www.npmjs.com/package/d3) which lacks its own TypeScript information (though such details are available through the @types package).

If constructing your own library code and desiring to operate within a namespace akin to the validation example, you would use namespace D3 instead of declare namespace D3, while working in a .ts file rather than a .d.ts one. The first part of the documentation illustrates using namespaces within your TypeScript code, while the latter demonstrates providing TypeScript metadata for pure JavaScript code.

Answer 4

My understanding of TypeScript is that the example code provided does not actually generate or modify any JavaScript output. Instead, it consists of declarations that serve to assist in error checking by IntelliSense and the TypeScript compiler, without directly impacting the code itself. These declarations are meant for an "ambient" declaration file, which provides TypeScript definitions for regular JavaScript libraries, enabling TypeScript and IntelliSense to work with them as if they were native TypeScript files rather than plain JavaScript. When TypeScript encounters something without a corresponding declaration, it typically treats it as an "any" type.

For the mentioned library, it is recommended to utilize the existing type library (npm install --save-dev @types/d3). After installing both the library (npm install --save d3) and its types @types/d3, using import * as d3 from 'd3' in a .ts file (in Angular 5; other setups may vary) successfully brings in the object and type information. The contents of the types file will differ significantly from those in the TypeScript documentation example, but they all consist of declarations rather than executable code.

Regarding the edits

The file in question is not a primary TypeScript file but a declarations file outlining the "TypeScript shape" of a standard JavaScript library - essentially guiding how the TypeScript compiler and IntelliSense should interpret the structure of the JavaScript code if it were written in TypeScript. Despite appearances, the choice of naming it D3 was intentional. The .d.ts file aims to offer TypeScript metadata for a library like D3 (https://www.npmjs.com/package/d3) which lacks its own TypeScript information (though such details are available through the @types package).

If constructing your own library code and desiring to operate within a namespace akin to the validation example, you would use namespace D3 instead of declare namespace D3, while working in a .ts file rather than a .d.ts one. The first part of the documentation illustrates using namespaces within your TypeScript code, while the latter demonstrates providing TypeScript metadata for pure JavaScript code.

Answer 5

Answer №3

The declare namespace keyword serves to enhance or alter existing namespaces, often within the realm of external libraries or type declaration files. In this scenario, all elements contained within the declare namespace block are inherently available for use in other files.

In contrast, the namespace keyword establishes a fresh namespace. Under this circumstance, the elements defined within the namespace remain private by default and require the explicit use of the export keyword to grant access to them for referencing in alternate files.

To sum up, declare namespace is employed to adjust or expand preexisting namespaces, with all elements automatically becoming public. On the other hand, namespace is utilized to create a new namespace, necessitating manual exporting of elements to enable external accessibility.

Hopefully, this explanation sheds light on the disparity between declare namespace and namespace!

Answer 6

The declare namespace keyword serves to enhance or alter existing namespaces, often within the realm of external libraries or type declaration files. In this scenario, all elements contained within the declare namespace block are inherently available for use in other files.

In contrast, the namespace keyword establishes a fresh namespace. Under this circumstance, the elements defined within the namespace remain private by default and require the explicit use of the export keyword to grant access to them for referencing in alternate files.

To sum up, declare namespace is employed to adjust or expand preexisting namespaces, with all elements automatically becoming public. On the other hand, namespace is utilized to create a new namespace, necessitating manual exporting of elements to enable external accessibility.

Hopefully, this explanation sheds light on the disparity between declare namespace and namespace!

Example of TypeScript Ambient Namespace Usage

Answer №1

Answer №2

Regarding the edits

Answer №3

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