Exports and export assignments are not permitted in module augmentations

问题

`
import { Request as ExpressRequest, Response as ExpressResponse } from 'express';
declare module 'kvl' {
    export = kvl;
}
declare const kvl : {
  ValidationDone:(param:(error: any, response: ExpressResponse) => void) => void;
}
`

Exports and export assignments are not permitted in module augmentations.

I was declared in .d.ts， Can't I use it like this?

回答1:

Module Augmentation:

Typescript calls this a module augmentation: You are using an existing module and add new definitions to it. Module augmentations have their own syntax:

the module that your declare must have the same name as the augmented module
inside the module you can't export anything

This is described here: https://github.com/Microsoft/TypeScript-Handbook/blob/fa9e2be1024014fe923d44b1b69d315e8347e444/pages/Declaration%20Merging.md#module-augmentation

Following the docs, your code becomes this:

// file1.ts
import { Request as ExpressRequest, Response as ExpressResponse } from 'express';

// module name must be "express"
declare module 'express' {

    // this can't be an export
    const kvl : {
        ValidationDone:(param:(error: any, response: ExpressResponse) => void) => void;
      }
}

Now you have augmented the express module and can use it like this:

// file2.ts
import {kvl} from "express";

// ...

Modular Declaration File:

If you don't want to inject your new types into the express module, you can use a declaration file for your new module. There are various types, a good overview can be found here: https://www.typescriptlang.org/docs/handbook/declaration-files/library-structures.html

Basically, you have to check how the code is used and then adapt your declarations to that. In your case, it looks like you want to import kvl as a module. So you can orient yourself on this sample file: https://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-d-ts.html

I have changed your code to the appropriate syntax. By the way, this is only correct in a .d.ts file:

//kvl.d.ts
import { Request as ExpressRequest, Response as ExpressResponse } from 'express';

export as namespace kvl;

export const kvl : {
    ValidationDone:(param:(error: any, response: ExpressResponse) => void) => void;
    };

Implementing a Module:

If kvl is your own code, then you don't have to work with declaration files. Typescript can analyze your modules. A module definition that would produce a kvl constant with proper type could look like this:

// kvl.ts
import { Request as ExpressRequest, Response as ExpressResponse } from 'express';
export const kvl : {
    ValidationDone:(param:(error: any, response: ExpressResponse) => void) => void;
    } = {ValidationDone: function(param){}};

Please note that modules automatically have their filename as modulename. Therefore, the above code should be in a file called kvl.ts.

来源：https://stackoverflow.com/questions/53186841/exports-and-export-assignments-are-not-permitted-in-module-augmentations

标签

typescript

express