打字稿声明合并：覆盖？

Question

Is there a way to "override" when doing declartion merge, eg:

app.ts (express + nodejs):

import * as express from 'express';
var app = express();

app.use(function(req, res, next) {
  console.log(req.headers.accept);
});

This fails with error:

error TS2339: Property 'accept' does not exist on type '{ [key: string]: string; }'.

Because in express.d.ts headers are declared like this:

headers: { [key: string]: string; };

So what i've tried to do, is create a definition of 'accept' :

declare module Express {
  export interface Headers {
    accept: String
  }
  export interface Request {
    headers: Headers
  }
}

But that does not work also (i can only add new members, not override them, right?):

    error TS2430: Interface 'e.Request' incorrectly extends interface 'Express.Request'.
  Types of property 'headers' are incompatible.
    Type '{ [key: string]: string; }' is not assignable to type 'Headers'.
      Property 'accept' is missing in type '{ [key: string]: string; }'.

So the only way to overcome this is change notation to:

req.headers.accept -> req.headers['accept']

Or i somehow can "redeclare" the headers property?

Answer 1

In Express, you can use the accepts method ( accepts documentation ):

if (req.accepts('json')) { //...

Or if you want them all, they are available as:

console.log(req.accepted);

To get other headers, use the get method ( get method documentation )

req.get('Content-Type');

These are all included the the type definition for Express on Definitely Typed .