How do I write a TypeScript declaration file for an external commonjs module that has constructor?

Question

PLEASE SEE MORE DETAILED QUESTION: How do I write a TypeScript declaration file for a complex external commonjs module that has constructor, such as imap?

I write TypeScript for a Node.js app, and I want to write a TypeScript declaration file for a javascript module (available from npm) that has a constructor at the module level.

Here is a simplified version of the relevant code, in file a.js:

function A(config) {
    this.state = 'constructed';
}
A.prototype.update = function() {
    this.state = 'updated';
};
module.exports = A;

and a simplified javascript application, app.js, that uses module a:

var mod = require('a');
var i = new mod({});
console.log('i.state=' + i.state);
i.update();
console.log('i.state=' + i.state);

How do I write a TypeScript declaration file for module a.js?

I've read the TypeScript Guide for Writing Definition (.d.ts) Files but unfortunately, I couldn't figure out how to apply the guidelines to this case.

updated to include interfaces

Here is my declaration file a.d.ts:

declare module 'a' {
    import events                           = require('events');
    import EventEmitter                     = events.EventEmitter;

    interface Config {
        foo: number;
    }
    interface Other {
        baz: number;
    }

    class A extends EventEmitter {
        state: string;
        constructor(config: Config);
        update(): void;
    }

    var out: typeof A;
    export = out;
}

I can't figure out how to make the interfaces available to my TypeScript app. I also want to keep them within the module, so that names like Config don't collide with those from other modules.

Added TypeScript app that uses this declaration

This is what I expect my app.ts to look like:

import mod = require('a');
import Config = mod.Config;
import Other = mod.Other;

var other : Other = {a: 2};
var config : Config = {foo: 2};
var i = new mod(config);
console.log('i.state=' + i.state)
i.update();
console.log('i.state=' + i.state)

wjohnsto · Accepted Answer · 2014-10-07 22:06:43Z

3

There are a couple ways to do this, here is one:

declare class A {
    state: string;
    constructor(config: any);
    update(): void;
}

declare module 'a' {
    var out: typeof A;

    export = out;
}

EDIT: If you want to include interfaces, but also have an exported class, you can set it up like this:

declare module A {
    class A {
        state: string;
        constructor();
        update(): void;
    }

    interface B {
        value: any;
    }
}

declare module 'a' {
    var out: typeof A.A;

    export = out;
}

edited Oct 7, 2014 at 22:06

answered Oct 7, 2014 at 20:51

wjohnsto

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4 Comments

psnider Over a year ago

I also tried moving the class declaration inside of the module (without the declare keyword), and that worked too.

psnider Over a year ago

I have a complication: How can I also define public interfaces in module a? It seems that the export = statment prevents this.

psnider Over a year ago

I can't get the answer with interfaces to work. I've added a typescript app.ts to the question. BTW, the compiler issues misleading error text in this case: "error TS2304: Cannot find name 'mod'.", when it cannot find Config or Other.

psnider Over a year ago

Thanks. This led me on the right path. I found another module, auth0, similar to the one I want to declare, and worked from the patterns there. Those patterns are similar to the ones you suggested.

psnider · Accepted Answer · 2014-10-07 23:56:44Z

I found an existing declaration file for a modules that has similar structure to the one for which I want to write a declaration file: auth0

I now have something that works, although not yet ideal. The declaration file a.d.ts is:

/// <reference path='node.d.ts' />
interface Config {
    foo: number;
}

declare module 'a' {
    import events                           = require('events');
    import EventEmitter                     = events.EventEmitter;

    class A extends EventEmitter {
        constructor(config : Config);
        state: string;
        update(): void;
    }
    var out: typeof A;
    export = out;
}

with the TypeScript app file app.ts being:

/// <reference path='a.d.ts' />
import mod = require('a');

var config : Config = {
    foo: 1
} 
var i = new mod(config);
console.log('i.state=' + i.state)
i.update();
console.log('i.state=' + i.state)

and the a.js module being as in the original question.

I compile this with: tsc --module commonjs app.ts

This certainly works for now.

Although I think it's messy to have the interface (Config) outside of the module, but I haven't yet figured out how to move the interfaces inside.

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