Extending typescript interface

Question

When extending the Express.Request interface in TypeScript I ran into this problem that I want to use an external library definition, but I can't import the external library as it results in error ->

Error:(4, 28) TS1147: Import declarations in an internal module cannot reference an external module.

Edit: It is a .d.ts file

/// <reference path="../typings/express/express.d.ts" />

declare module Express {
    import bunyan = require('bunyan'); <-- results in error
    export interface Request {
        _id: string; <-- this works
        log: bunyan.Logger; <-- Here I want to define that it is bunyan.Logger instance;
    }
}

Trying to reference the bunyan.d.ts (https://github.com/borisyankov/DefinitelyTyped/blob/master/bunyan/bunyan.d.ts) Also results in a problem, as the bunyan module is exported as string

declare module "bunyan" {
...
}

As such trying to use it from reference results in not found.

/// <reference path="../typings/express/express.d.ts" />
/// <reference path="../typings/bunyan/bunyan.d.ts" />

declare module Express {
    export interface Request {
        _id: string;
        log: bunyan.Logger; <- Error:(8, 18) TS2304: Cannot find name 'bunyan'.
    }
}

tl;dr; How to extend interface definition with external module definitions.

@Tarh Error:(4, 1) TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file. — DeadAlready
– DeadAlready, Commented Apr 8, 2015 at 14:04
OK. The require misled me, I believed it was a .ts file. — Paleo
– Paleo, Commented Apr 8, 2015 at 14:10
A suggestion: if a file .d.ts exists for the external module bunyan, you can reference it with /// <reference ... and then use it to type Request.log. — Paleo
– Paleo, Commented Apr 8, 2015 at 14:13
External modules are not namespaces. Try to use Logger instead of bunyan.Logger. If it still not works, then you can try to upgrade to typescript 1.5-alpha and to use the external module import syntax. Or edit the .d.ts file and remove the quotes in declare module "bunyan" => declare module bunyan. Without quotes, bunyan becomes a namespace and bunyan.Logger becomes available. — Paleo
– Paleo, Commented Apr 8, 2015 at 15:31

David Sherret · Accepted Answer · 2015-04-08 17:31:08Z

3

I don't think you can add to an existing interface when a require is necessary, but you can extend the existing interface using the extends keyword.

Move your import statement outside your module, export your module, and extend the existing interface:

import bunyan = require('bunyan');
import express = require('express');

export declare module ExtendedExpress {
    export interface Request extends express.Express.Request {
        _id: string;
        log: bunyan.Logger;
    }
}

Then you have to import this module where you want to use it.

edited Apr 8, 2015 at 17:31

answered Apr 8, 2015 at 14:03

David Sherret

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3 Comments

DeadAlready Over a year ago

Adding an import outside the declare function causes all the extensions being lost. (The fail is as if not referenced at all) Error:(71, 9) TS2339: Property '_id' does not exist on type 'Request'.

DeadAlready Over a year ago

Yes, I can extend this way creating a new interface with a different name. Not what I want though -> The express module has internal RequestHandler interface that uses the Request interface. By creating a new interface I would have to import and define on every route handler that the parameters are of the new interface not the old - very cumbersome. Whereas extending the old interface gives me this information automatically.

David Sherret Over a year ago

@DeadAlready if you really want to do what you want, then I think you have to edit the original express.d.ts directly. There's a few guys who frequent the typescript tag and they're more knowledge than me on this so they'll probably be able to give a more definitive answer.

Brocco · Accepted Answer · 2015-04-08 14:01:02Z

1

The referencing of internal and external modules will be improved in v1.5 which is currently in an alpha release (http://blogs.msdn.com/b/typescript/archive/2015/03/27/announcing-typescript-1-5-alpha.aspx).

In the meantime you can import in your bunyan module via:

var bunyan = require('bunyan');

answered Apr 8, 2015 at 14:01

Brocco

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1 Comment

DeadAlready Over a year ago

Error:(4, 16) TS1039: Initializers are not allowed in ambient contexts.

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