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Express's `Middleware` type is not correct

See original GitHub issue

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

https://github.com/flowtype/flow-typed/blob/master/definitions/npm/express_v4.x.x/flow_v0.25.x-/express_v4.x.x.js#L90

I don’t know how flow handle union type of function. But according to the doc and variance rule, Middleware should be an intersection type, not union type.

Issue Analytics

State:
Created 7 years ago
Reactions:1
Comments:16 (7 by maintainers)

Top GitHub Comments

1reaction

richardscarrottcommented, Nov 12, 2016

@vkurchatkin Is there no way for flow to determine the types based on arity?

0reactions

pascalduezcommented, Aug 16, 2019

Is this issue still happening with the very latest version of the definition?

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