Expanding TypeScript Definitions

Question

Expanding TypeScript Definitions

I've been experimenting with TypeScript and Express. After importing type declarations from Typings, I found the following code:

// Imported from typings
// Source: https://raw.githubusercontent.com/DefinitelyTyped/DefinitelyTyped/7de6c3dd94feaeb21f20054b9f30d5dabc5efabd/express/express.d.ts
declare module "express" {
    import * as serveStatic from "serve-static";
    import * as core from "express-serve-static-core";

    /**
     * Initializes an Express application using the express() function.
     */
    function e(): core.Express;

    namespace e {

        var static: typeof serveStatic;

        export function Router(options?: any): core.Router;

        // Additional interfaces and types here...
        
        interface Send extends core.Send { }
    }

    export = e;
}

Next, I wanted to enhance all Response objects with a new method:

const express = require('express');
express.response.sendWrapped = function(obj: Object, meta?: Object) {
    return this.json({
        data: obj
    });
};

However, I'm now faced with the task of incorporating this extension into the existing typings. My goal is to modify the definition without altering the original typings or affecting other parts of the code that rely on Response. How can I achieve this in a clean and efficient manner?

express typescript typescript-typings

Answer 1

Answer №1

If you're using TypeScript 2.0 or a pre-release version like typescript@next, you have the ability to leverage module augmentation syntax. This allows you to enhance the definition of express by adding your custom response definition:

import express = require('express');

declare module "express" {
    namespace response {
        function sendWrapped(obj: any, meta?: any): void;
    }
}

express.response.sendWrapped = function(obj: Object, meta?: Object) {
    return this.json({
        data: obj
    });
};

Answer 2

If you're using TypeScript 2.0 or a pre-release version like typescript@next, you have the ability to leverage module augmentation syntax. This allows you to enhance the definition of express by adding your custom response definition:

import express = require('express');

declare module "express" {
    namespace response {
        function sendWrapped(obj: any, meta?: any): void;
    }
}

express.response.sendWrapped = function(obj: Object, meta?: Object) {
    return this.json({
        data: obj
    });
};

Answer 3

Answer №2

Here are a few points to consider:

(1) The correct syntax should be express.Response.sendWrapped, not response.

(2) It seems that you added the sendWrapped function directly to the Response class, rather than extending its prototype. If you want to extend the prototype, the code should look like this:

express.Response.prototype.sendWrapped = function(obj: Object, meta?: Object) {
    return this.json({
        data: obj
    });
};

(3) Alternatively, you can add to an existing type using namespaces as shown below:

namespace express {
    interface Response {
        sendWrapped(obj: Object, meta?: Object): any;
    }
}

For more information, refer to Declaration Merging

Edit

If you're working with a d.ts file, make sure to declare the namespace properly:

declare namespace express {
    ...
}

If you prefer a more robust solution, consider extending express.Response as demonstrated below:

class MyResponse extends express.Response {
    constructor() {
        super();
    }

    sendWrapped(obj: Object, meta?: Object): express.Response {
        return this.json({
            data: obj
        });
    }
}

This approach is less dependent on possible changes in the express API and aligns better with object-oriented principles.

Answer 4

Here are a few points to consider:

(1) The correct syntax should be express.Response.sendWrapped, not response.

(2) It seems that you added the sendWrapped function directly to the Response class, rather than extending its prototype. If you want to extend the prototype, the code should look like this:

express.Response.prototype.sendWrapped = function(obj: Object, meta?: Object) {
    return this.json({
        data: obj
    });
};

(3) Alternatively, you can add to an existing type using namespaces as shown below:

namespace express {
    interface Response {
        sendWrapped(obj: Object, meta?: Object): any;
    }
}

For more information, refer to Declaration Merging

Edit

If you're working with a d.ts file, make sure to declare the namespace properly:

declare namespace express {
    ...
}

If you prefer a more robust solution, consider extending express.Response as demonstrated below:

class MyResponse extends express.Response {
    constructor() {
        super();
    }

    sendWrapped(obj: Object, meta?: Object): express.Response {
        return this.json({
            data: obj
        });
    }
}

This approach is less dependent on possible changes in the express API and aligns better with object-oriented principles.

Expanding TypeScript Definitions

Answer №1

Answer №2

Edit

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