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formidable npm version MIT license Libera Manifesto Twitter

A Node.js module for parsing form data, especially file uploads.

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If you have any how-to kind of questions, please read the Contributing Guide and Code of Conduct documents.
For bugs reports and feature requests, please create an issue or ping @tunnckoCore at Twitter.

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Status: Maintained npm version

This module was initially developed by @felixge for Transloadit, a service focused on uploading and encoding images and videos. It has been battle-tested against hundreds of GBs of file uploads from a large variety of clients and is considered production-ready and is used in production for years.

Currently, we are few maintainers trying to deal with it. :) More contributors are always welcome! ❤️ Jump on issue #412 which is closed, but if you are interested we can discuss it and add you after strict rules, like enabling Two-Factor Auth in your npm and GitHub accounts.

Note: The github master branch is a "canary" branch - try it with npm i [email protected]. Do not expect (for now) things from it to be inside thelatest "dist-tag" in the Npm. The[email protected]is thev1.2.1 version and probably it will be the lastv1 release!

Note: v2 is coming soon!



This project requires Node.js >= 10.13. Install it using yarn or npm.
We highly recommend to use Yarn when you think to contribute to this project.

npm install formidable
# or the canary version
npm install [email protected]

or with Yarn v1/v2

yarn add formidable
# or the canary version
yarn add [email protected]

This is a low-level package, and if you're using a high-level framework it may already be included. Check the examples below and the examples/ folder.


For more examples look at the examples/ directory.

with Node.js http module

Parse an incoming file upload, with the Node.js's built-in http module.

const http = require('http');
const formidable = require('formidable');

const server = http.createServer((req, res) => {
  if (req.url === '/api/upload' && req.method.toLowerCase() === 'post') {
    // parse a file upload
    const form = formidable({ multiples: true });

    form.parse(req, (err, fields, files) => {
      if (err) {
        res.writeHead(err.httpCode || 400, { 'Content-Type': 'text/plain' });
      res.writeHead(200, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ fields, files }, null, 2));


  // show a file upload form
  res.writeHead(200, { 'Content-Type': 'text/html' });
    <h2>With Node.js <code>"http"</code> module</h2>
    <form action="/api/upload" enctype="multipart/form-data" method="post">
      <div>Text field title: <input type="text" name="title" /></div>
      <div>File: <input type="file" name="multipleFiles" multiple="multiple" /></div>
      <input type="submit" value="Upload" />

server.listen(8080, () => {
  console.log('Server listening on http://localhost:8080/ ...');

with Express.js

There are multiple variants to do this, but Formidable just need Node.js Request stream, so something like the following example should work just fine, without any third-party Express.js middleware.

Or try the examples/with-express.js

const express = require('express');
const formidable = require('formidable');

const app = express();

app.get('/', (req, res) => {
    <h2>With <code>"express"</code> npm package</h2>
    <form action="/api/upload" enctype="multipart/form-data" method="post">
      <div>Text field title: <input type="text" name="title" /></div>
      <div>File: <input type="file" name="someExpressFiles" multiple="multiple" /></div>
      <input type="submit" value="Upload" />
});'/api/upload', (req, res, next) => {
  const form = formidable({ multiples: true });

  form.parse(req, (err, fields, files) => {
    if (err) {
    res.json({ fields, files });

app.listen(3000, () => {
  console.log('Server listening on http://localhost:3000 ...');

with Koa and Formidable

Of course, with Koa v1, v2 or future v3 the things are very similar. You can use formidable manually as shown below or through the koa-better-body package which is using formidable under the hood and support more features and different request bodies, check its documentation for more info.

Note: this example is assuming Koa v2. Be aware that you should pass ctx.req which is Node.js's Request, and NOT the ctx.request which is Koa's Request object - there is a difference.

const Koa = require('koa');
const formidable = require('formidable');

const app = new Koa();

app.on('error', (err) => {
  console.error('server error', err);

app.use(async (ctx, next) => {
  if (ctx.url === '/api/upload' && ctx.method.toLowerCase() === 'post') {
    const form = formidable({ multiples: true });

    // not very elegant, but that's for now if you don't want to use `koa-better-body`
    // or other middlewares.
    await new Promise((resolve, reject) => {
      form.parse(ctx.req, (err, fields, files) => {
        if (err) {

        ctx.set('Content-Type', 'application/json');
        ctx.status = 200;
        ctx.state = { fields, files };
        ctx.body = JSON.stringify(ctx.state, null, 2);
    await next();

  // show a file upload form
  ctx.set('Content-Type', 'text/html');
  ctx.status = 200;
  ctx.body = `
    <h2>With <code>"koa"</code> npm package</h2>
    <form action="/api/upload" enctype="multipart/form-data" method="post">
    <div>Text field title: <input type="text" name="title" /></div>
    <div>File: <input type="file" name="koaFiles" multiple="multiple" /></div>
    <input type="submit" value="Upload" />

app.use((ctx) => {
  console.log('The next middleware is called');
  console.log('Results:', ctx.state);

app.listen(3000, () => {
  console.log('Server listening on http://localhost:3000 ...');


The benchmark is quite old, from the old codebase. But maybe quite true though. Previously the numbers was around ~500 mb/sec. Currently with moving to the new Node.js Streams API it's faster. You can clearly see the differences between the Node versions.

Note: a lot better benchmarking could and should be done in future.

Benchmarked on 8GB RAM, Xeon X3440 (2.53 GHz, 4 cores, 8 threads)

~/github/node-formidable master
❯ nve --parallel 8 10 12 13 node benchmark/bench-multipart-parser.js

 ⬢  Node 8

1261.08 mb/sec

 ⬢  Node 10

1113.04 mb/sec

 ⬢  Node 12

2107.00 mb/sec

 ⬢  Node 13

2566.42 mb/sec

benchmark January 29th, 2020


Formidable / IncomingForm

All shown are equivalent.

Please pass options to the function/constructor, not by assigning them to the instance form

const formidable = require('formidable');
const form = formidable(options);

// or
const { formidable } = require('formidable');
const form = formidable(options);

// or
const { IncomingForm } = require('formidable');
const form = new IncomingForm(options);

// or
const { Formidable } = require('formidable');
const form = new Formidable(options);


See it's defaults in src/Formidable.js DEFAULT_OPTIONS (the DEFAULT_OPTIONS constant).

  • options.encoding {string} - default 'utf-8'; sets encoding for incoming form fields,

  • options.uploadDir {string} - default os.tmpdir(); the directory for placing file uploads in. You can move them later by using fs.rename().

  • options.keepExtensions {boolean} - default false; to include the extensions of the original files or not

  • options.allowEmptyFiles {boolean} - default true; allow upload empty files

  • options.minFileSize {number} - default 1 (1byte); the minium size of uploaded file.

  • options.maxFileSize {number} - default 200 * 1024 * 1024 (200mb); limit the size of uploaded file.

  • options.maxFields {number} - default 1000; limit the number of fields, set 0 for unlimited

  • options.maxFieldsSize {number} - default 20 * 1024 * 1024 (20mb); limit the amount of memory all fields together (except files) can allocate in bytes.

  • options.hashAlgorithm {string | false} - default false; include checksums calculated for incoming files, set this to some hash algorithm, see crypto.createHash for available algorithms

  • options.fileWriteStreamHandler {function} - default null, which by default writes to host machine file system every file parsed; The function should return an instance of a Writable stream that will receive the uploaded file data. With this option, you can have any custom behavior regarding where the uploaded file data will be streamed for. If you are looking to write the file uploaded in other types of cloud storages (AWS S3, Azure blob storage, Google cloud storage) or private file storage, this is the option you're looking for. When this option is defined the default behavior of writing the file in the host machine file system is lost.

  • options.multiples {boolean} - default false; when you call the .parse method, the files argument (of the callback) will contain arrays of files for inputs which submit multiple files using the HTML5 multiple attribute. Also, the fields argument will contain arrays of values for fields that have names ending with '[]'.

  • options.filename {function} - default undefined Use it to control newFilename. Must return a string. Will be joined with options.uploadDir.

  • options.filter {function} - default function that always returns true. Use it to filter files before they are uploaded. Must return a boolean.

options.filename {function} function (name, ext, part, form) -> string

Note: If this size of combined fields, or size of some file is exceeded, an 'error' event is fired.

// The amount of bytes received for this form so far.
// The expected number of bytes in this form.

options.filter {function} function ({name, originalFilename, mimetype}) -> boolean

Note: use an outside variable to cancel all uploads upon the first error

const options = {
  filter: function ({name, originalFilename, mimetype}) {
    // keep only images
    return mimetype && mimetype.includes("image");

.parse(request, callback)

Parses an incoming Node.js request containing form data. If callback is provided, all fields and files are collected and passed to the callback.

const formidable = require('formidable');

const form = formidable({ multiples: true, uploadDir: __dirname });

form.parse(req, (err, fields, files) => {
  console.log('fields:', fields);
  console.log('files:', files);

You may overwrite this method if you are interested in directly accessing the multipart stream. Doing so will disable any 'field' / 'file' events processing which would occur otherwise, making you fully responsible for handling the processing.

About uploadDir, given the following directory structure

├── src
│   └── server.js
└── uploads
    └── image.jpg

__dirname would be the same directory as the source file itself (src)


to put files in uploads.

Omitting __dirname would make the path relative to the current working directory. This would be the same if server.js is launched from src but not project-name.

null will use default which is os.tmpdir()

Note: If the directory does not exist, the uploaded files are silently discarded. To make sure it exists:

import {createNecessaryDirectoriesSync} from "filesac";

const uploadPath = `${__dirname}/../uploads`;

In the example below, we listen on couple of events and direct them to the data listener, so you can do whatever you choose there, based on whether its before the file been emitted, the header value, the header name, on field, on file and etc.

Or the other way could be to just override the form.onPart as it's shown a bit later.

form.once('error', console.error);

form.on('fileBegin', (formname, file) => {
  form.emit('data', { name: 'fileBegin', formname, value: file });

form.on('file', (formname, file) => {
  form.emit('data', { name: 'file', formname, value: file });

form.on('field', (fieldName, fieldValue) => {
  form.emit('data', { name: 'field', key: fieldName, value: fieldValue });

form.once('end', () => {

// If you want to customize whatever you want...
form.on('data', ({ name, key, value, buffer, start, end, formname, ...more }) => {
  if (name === 'partBegin') {
  if (name === 'partData') {
  if (name === 'headerField') {
  if (name === 'headerValue') {
  if (name === 'headerEnd') {
  if (name === 'headersEnd') {
  if (name === 'field') {
    console.log('field name:', key);
    console.log('field value:', value);
  if (name === 'file') {
    console.log('file:', formname, value);
  if (name === 'fileBegin') {
    console.log('fileBegin:', formname, value);

.use(plugin: Plugin)

A method that allows you to extend the Formidable library. By default we include 4 plugins, which esentially are adapters to plug the different built-in parsers.

The plugins added by this method are always enabled.

See src/plugins/ for more detailed look on default plugins.

The plugin param has such signature:

function(formidable: Formidable, options: Options): void;

The architecture is simple. The plugin is a function that is passed with the Formidable instance (the form across the README examples) and the options.

Note: the plugin function's this context is also the same instance.

const formidable = require('formidable');

const form = formidable({ keepExtensions: true });

form.use((self, options) => {
  // self === this === form
  console.log('woohoo, custom plugin');
  // do your stuff; check `src/plugins` for inspiration

form.parse(req, (error, fields, files) => {

Important to note, is that inside plugin this.options, self.options and options MAY or MAY NOT be the same. General best practice is to always use the this, so you can later test your plugin independently and more easily.

If you want to disable some parsing capabilities of Formidable, you can disable the plugin which corresponds to the parser. For example, if you want to disable multipart parsing (so the src/parsers/Multipart.js which is used in src/plugins/multipart.js), then you can remove it from the options.enabledPlugins, like so

const { Formidable } = require('formidable');

const form = new Formidable({
  hashAlgorithm: 'sha1',
  enabledPlugins: ['octetstream', 'querystring', 'json'],

Be aware that the order MAY be important too. The names corresponds 1:1 to files in src/plugins/ folder.

Pull requests for new built-in plugins MAY be accepted - for example, more advanced querystring parser. Add your plugin as a new file in src/plugins/ folder (lowercased) and follow how the other plugins are made.


If you want to use Formidable to only handle certain parts for you, you can do something similar. Or see #387 for inspiration, you can for example validate the mime-type.

const form = formidable();

form.onPart = (part) => {
  part.on('data', (buffer) => {
    // do whatever you want here

For example, force Formidable to be used only on non-file "parts" (i.e., html fields)

const form = formidable();

form.onPart = function (part) {
  // let formidable handle only non-file parts
  if (part.originalFilename === '' || !part.mimetype) {
    // used internally, please do not override!


export interface File {
  // The size of the uploaded file in bytes.
  // If the file is still being uploaded (see `'fileBegin'` event),
  // this property says how many bytes of the file have been written to disk yet.
  file.size: number;

  // The path this file is being written to. You can modify this in the `'fileBegin'` event in
  // case you are unhappy with the way formidable generates a temporary path for your files.
  file.filepath: string;

  // The name this file had according to the uploading client. string | null;

  // The mime type of this file, according to the uploading client.
  file.type: string | null;

  // A Date object (or `null`) containing the time this file was last written to.
  // Mostly here for compatibility with the [W3C File API Draft](
  file.lastModifiedDate: Date | null;

  file.hashAlgorithm: false | |'sha1' | 'md5' | 'sha256'
  // If `options.hashAlgorithm` calculation was set, you can read the hex digest out of this var.
  file.hash: string | object | null;


This method returns a JSON-representation of the file, allowing you to JSON.stringify() the file which is useful for logging and responding to requests.



Emitted after each incoming chunk of data that has been parsed. Can be used to roll your own progress bar.

form.on('progress', (bytesReceived, bytesExpected) => {});


Emitted whenever a field / value pair has been received.

form.on('field', (name, value) => {});


Emitted whenever a new file is detected in the upload stream. Use this event if you want to stream the file to somewhere else while buffering the upload on the file system.

form.on('fileBegin', (formName, file) => {
    // accessible here 
    // formName the name in the form (<input name="thisname" type="file">) or http filename for octetstream
    // file.originalFilename http filename or null if there was a parsing error
    // file.newFilename generated hexoid or what options.filename returned
    // file.filepath default pathnme as per options.uploadDir and options.filename
    // file.filepath = CUSTOM_PATH // to change the final path


Emitted whenever a field / file pair has been received. file is an instance of File.

form.on('file', (formname, file) => {
    // same as fileBegin, except
    // it is too late to change file.filepath
    // file.hash is available if options.hash was used


Emitted when there is an error processing the incoming form. A request that experiences an error is automatically paused, you will have to manually call request.resume() if you want the request to continue firing 'data' events.

May have error.httpCode and error.code attached.

form.on('error', (err) => {});


Emitted when the request was aborted by the user. Right now this can be due to a 'timeout' or 'close' event on the socket. After this event is emitted, an error event will follow. In the future there will be a separate 'timeout' event (needs a change in the node core).

form.on('aborted', () => {});


Emitted when the entire request has been received, and all contained files have finished flushing to disk. This is a great place for you to send your response.

form.on('end', () => {});

Ports & Credits


If the documentation is unclear or has a typo, please click on the page's Edit button (pencil icon) and suggest a correction. If you would like to help us fix a bug or add a new feature, please check our Contributing Guide. Pull requests are welcome!

Thanks goes to these wonderful people (emoji key):

Felix Geisendörfer

💻 🎨 🤔 📖

Charlike Mike Reagent

🐛 🚇 🎨 💻 📖 💡 🤔 🚧 ⚠️


💻 ⚠️ 💬 🐛

Walle Cyril

💬 🐛 💻 💵 🤔 🚧


💬 🐛 💻 🚧


💬 🐛 💻


💬 🐛 💻 🤔 🚧

Dylan Piercey


Adam Dobrawy

🐛 📖



Jesse Feng


Nathanael Demacon

💬 💻 👀



Gabriel Petrovay

🐛 💻

Philip Woods

💻 🤔

Dmitry Ivonin


Claudio Poli


From a Felix blog post:

  • Sven Lito for fixing bugs and merging patches
  • egirshov for contributing many improvements to the node-formidable multipart parser
  • Andrew Kelley for also helping with fixing bugs and making improvements
  • Mike Frey for contributing JSON support


Formidable is licensed under the MIT License.

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