Created
April 17, 2020 02:06
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type Middleware<In, Out> = <T extends In>(req: Request, res: Response, state: T) => Promise<T & Out>; | |
export const fooMiddleware: Middleware<{}, { foo: string }> = async (req, res, state) => { | |
return { ...state, foo: "foo" }; | |
}; | |
export const barMiddleware: Middleware<{}, { bar: string }> = async (req, res, state) => { | |
return { ...state, bar: "bar" }; | |
}; | |
export const foobarMiddleware: Middleware<{ foo: string; bar: string }, {}> = async (req, res, state) => { | |
res.send(`hello ${state.foo} ${state.bar}`); | |
return state; | |
}; | |
const pipe = (...middlewares: Middleware<any, any>[]) => async (req: Request, res: Response) => { | |
middlewares.reduce( | |
async (statePromise, middleware) => await middleware(req, res, await statePromise), | |
Promise.resolve({}) | |
); | |
}; | |
// This is typesafe | |
app.get("/", async (req: Request, res: Response) => { | |
await foobarMiddleware(req, res, await barMiddleware(req, res, await fooMiddleware(req, res, {}))); | |
}); | |
// This is not :( | |
app.get("/", pipe(fooMiddleware, barMiddleware, foobarMiddleware)); |
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