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Express' Request and Response types don't work for middlewares or routes.

See original GitHub issue

I’m trying to type express middlewares, but if I omit the type signature they end up being any:

/* @flow weak */

const express = require('express')
const router = new express.Router()

router.get('/', function (req, res) {
})

$ flow type-at-pos router.js 6 28
any
/home/despairblue/git/wunderflats/api/router.js:6:27,6:29

And annotating them using the Request and Response classes from the express libdef leads to this:

/* @flow weak */

const express = require('express')
const router = new express.Router()

router.get('/', function (req /* : Request */, res /* : Response */) {
})

router.js:6
  6: router.get('/', function (req /* : Request */, res /* : Response */) {
     ^ call of method `get`
  6: router.get('/', function (req /* : Request */, res /* : Response */) {
     ^ call of method `get`. Function cannot be called on any member of intersection type
 92:     (middleware: Middleware): T;
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ intersection. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:92
  Member 1:
   92:     (middleware: Middleware): T;
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:92
  Error:
    6: router.get('/', function (req /* : Request */, res /* : Response */) {
                  ^^^ string. This type is incompatible with
   92:     (middleware: Middleware): T;
                        ^^^^^^^^^^ union: function type(s). See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:92
    Member 1:
     89:     ((req: Request, res: Response, next: NextFunction) => mixed) |
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:89
    Error:
      6: router.get('/', function (req /* : Request */, res /* : Response */) {
                    ^^^ string. This type is incompatible with
     89:     ((req: Request, res: Response, next: NextFunction) => mixed) |
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:89
    Member 2:
     90:     ((error: ?Error, req : Request, res: Response, next: NextFunction) => mixed);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:90
    Error:
      6: router.get('/', function (req /* : Request */, res /* : Response */) {
                    ^^^ string. This type is incompatible with
     90:     ((error: ?Error, req : Request, res: Response, next: NextFunction) => mixed);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:90
  Member 2:
   93:     (...middleware: Array<Middleware>): T;
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:93
  Error:
    6: router.get('/', function (req /* : Request */, res /* : Response */) {
                  ^^^ string. This type is incompatible with
   93:     (...middleware: Array<Middleware>): T;
                                 ^^^^^^^^^^ union: function type(s). See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:93
    Member 1:
     89:     ((req: Request, res: Response, next: NextFunction) => mixed) |
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:89
    Error:
      6: router.get('/', function (req /* : Request */, res /* : Response */) {
                    ^^^ string. This type is incompatible with
     89:     ((req: Request, res: Response, next: NextFunction) => mixed) |
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:89
    Member 2:
     90:     ((error: ?Error, req : Request, res: Response, next: NextFunction) => mixed);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:90
    Error:
      6: router.get('/', function (req /* : Request */, res /* : Response */) {
                    ^^^ string. This type is incompatible with
     90:     ((error: ?Error, req : Request, res: Response, next: NextFunction) => mixed);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:90
  Member 3:
   94:     (path: string|RegExp, ...middleware: Array<Middleware>): T;
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:94
  Error:
    6: router.get('/', function (req /* : Request */, res /* : Response */) {
                       ^ function. This type is incompatible with
   94:     (path: string|RegExp, ...middleware: Array<Middleware>): T;
                                                      ^^^^^^^^^^ union: function type(s). See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:94
    Member 1:
     89:     ((req: Request, res: Response, next: NextFunction) => mixed) |
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:89
    Error:
     89:     ((req: Request, res: Response, next: NextFunction) => mixed) |
                    ^^^^^^^ Request. This type is incompatible with. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:89
      6: router.get('/', function (req /* : Request */, res /* : Response */) {
                                            ^^^^^^^ Request
    Member 2:
     90:     ((error: ?Error, req : Request, res: Response, next: NextFunction) => mixed);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:90
    Error:
      6: router.get('/', function (req /* : Request */, res /* : Response */) {
                                            ^^^^^^^ Request. This type is incompatible with
     90:     ((error: ?Error, req : Request, res: Response, next: NextFunction) => mixed);
                       ^^^^^ null. See lib: flow-typed/express_v4.x.x/flow_>=v0.25.x/express_v4.x.x.js:90

Versions:

flow: 0.30.0

Issue Analytics

State:
Created 7 years ago
Reactions:4
Comments:7 (7 by maintainers)

Top GitHub Comments

21reactions

shuheicommented, Feb 1, 2017

Without changing the libdef, the following is working for me on flow 0.38.0:

router.get('/', function (req: express$Request, res) {
})

import type { $Request } from 'express';

router.get('/', function (req: $Request, res) {
})

3reactions

jamiebuildscommented, Sep 12, 2016

I have a different set of issues when I try it out that come down to the definition of Middleware

It seems that it’s using a union type (A | B) instead of an intersection type (A & B).

However I don’t know where in the express api you have this.

Changing the definition of Middleware to the following seems to fix everything:

declare type Middleware = ((req: Request, res: Response, next: NextFunction) => mixed);

[try]

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