Typesafe Express Shit

app.ts

import Express from 'express'
import { Application, NextFunction, Request, Response } from 'express'
import y from 'yup'
export interface TypedRequest<TBody> extends Request {
    body: TBody
}

export interface TypedResponse<TBody> extends Response {
    json: (body: TBody) => Response
}

const PostEmailRequestSchema = y.object().shape({
    subject: y.string().required(),
    to: y.array(y.string()).required(),
    cc: y.array(y.string()).optional(),
    bcc: y.array(y.string()).optional(),
})

const PostEmailResponseSchema = y.object().shape({
    message: y.string().required(),
    id: y.string().required(),
})

type PostEmailRequest = {
    subject: string
    to: string[]
    cc?: string[]
    bcc?: string[]
}
type PostEmailResponse = { id: string; message: string }

const PostEmailHandler = async (
    req: TypedRequest<PostEmailRequest>,
    res: TypedResponse<PostEmailResponse>,
    next: NextFunction
) => {
    const postBody = req.body
    const isValid = await PostEmailRequestSchema.isValid(postBody)
    if (!isValid) {
        res.statusCode = 400
        return next()
    }
    res.statusCode = 201
    const response: PostEmailResponse = {
        id: new Date().getUTCMilliseconds().toString(),
        message: 'Accepted',
    }
    const isResponseValid = await PostEmailResponseSchema.isValid(response)
    if(isResponseValid) {
        res.json(response)
        return next()
    }
    throw new Error('This api is shit but typesafe')
}

const router = Express.Router()
router.post('/email', PostEmailHandler)

const emailApp: Application = Express()
emailApp.use(router)
const PORT = 3333
emailApp.listen(PORT, () => `📧 Email API Started on http://localhost:${PORT}`)