Using multer diskStorage with Typescript

I'm translating a node.js server to typescript.

My funcion with node is:

const storage = multer.diskStorage({
    destination: function (req, file, cb) {
        const dir = './uploads/';
        mkdirp(dir, err => cb(err, dir));
    },
    filename: function (req, file, cb) {
        cb(null, file.originalname)
    }
});

const upload = multer({
    storage: storage
});

router.post('/test', upload.fields({name: 'image'}), async function (req, res, next) {
...
});

But I have a lot of errors. For example I can't set the file argument as Express.File type, 'memoryStorage' does not accept arguments or mkdirp tells me that is not callable.

Here's how I did it using the type definitions in the @types/multer.

If you haven't already, first install the type definitions for the multer package:

npm i --save-dev @types/multer

Imports and type aliases

import { Request } from 'express'
import multer, { FileFilterCallback } from 'multer'

type DestinationCallback = (error: Error | null, destination: string) => void
type FileNameCallback = (error: Error | null, filename: string) => void

For storage

export const fileStorage = multer.diskStorage({
    destination: (
        request: Request,
        file: Express.Multer.File,
        callback: DestinationCallback
    ): void => {
        // ...Do your stuff here.
    },

    filename: (
        req: Request, 
        file: Express.Multer.File, 
        callback: FileNameCallback
    ): void => {
        // ...Do your stuff here.
    }
})

For fileFilter

export const fileFilter = (
    request: Request,
    file: Express.Multer.File,
    callback: FileFilterCallback
): void => {
    if (
        file.mimetype === 'image/png' ||
        file.mimetype === 'image/jpg' ||
        file.mimetype === 'image/jpeg'
    ) {
        callback(null, true)
    } else {
        callback(null, false)
    }
}

For cleaner code and separation of concerns, place the above two constants in a separate file like config/multer.ts or util/multer.ts

Usage

Import and use the above constants in app.ts or server.ts:

app.use(multer({ storage: fileStorage, fileFilter: fileFilter })