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File upload in Next.js and TypeScript

jtfinlay profile image James Finlay ・2 min read

Original post

Sharing the solution of how to create an API in Next.js that supports file upload. I hit issues that are sorted out by this implementation.

This solution uses multer to handle multipart/form-data uploads.

We first set up a helper method that will invoke middleware before the operation, and throw an error if the middleware fails.

import type { NextApiRequest, NextApiResponse } from 'next';

export default function initMiddleware(middleware: any) {
    return (req: NextApiRequest, res: NextApiResponse) =>
      new Promise((resolve, reject) => {
        middleware(req, res, (result) => {
            if (result instanceof Error) {
                return reject(result);
            return resolve(result);
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The implementation has a few key pieces:

  1. BodyParser is disabled (Next.js enables this by default). Otherwise, multer is unable to process the files and the files are not placed in the request.
  2. The files are available in the request. In this scenario, it is a video Blob with a Buffer within. This may vary by file type.
import type { NextApiRequest, NextApiResponse } from 'next';
import multer from 'multer';
import initMiddleware from '../../lib/init-middleware';

const upload = multer();

// for parsing multipart/form-data
// note that Multer limits to 1MB file size by default
const multerAny = initMiddleware(

type NextApiRequestWithFormData = NextApiRequest & {
    files: any[],

type BlobCorrected = Blob & {
    buffer: Buffer,

// Doc on custom API configuration:
export const config = {
    api: {
        bodyParser: false,

export default async (req: NextApiRequestWithFormData, res: NextApiResponse) => {
    await multerAny(req, res);

    // This operation expects a single file upload. Edit as needed.
    if (!req.files?.length || req.files.length > 1) {
        res.statusCode = 400;

    const blob: BlobCorrected = req.files[0];

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Thank you! This behavior used on ClippyTeams (a side project to build a Stories clone in Microsoft Teams). Feel free to fork and explore.

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