1.0.18 • Public • Published


Build Status


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

Current status

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


  • Fast (~500mb/sec), non-buffering multipart parser
  • Automatically writing file uploads to disk
  • Low memory footprint
  • Graceful error handling
  • Very high test coverage


This is a low level package, and if you're using a high level framework such as Express, chances are it's already included in it. You can read this discussion about how Formidable is integrated with Express.

Via npm:

npm install formidable@latest


git clone git:// formidable
vim my.js
# var formidable = require('./formidable');

Note: Formidable requires gently to run the unit tests, but you won't need it for just using the library.


Parse an incoming file upload.

var formidable = require('formidable'),
    http = require('http'),
    util = require('util');
http.createServer(function(req, res) {
  if (req.url == '/upload' && req.method.toLowerCase() == 'post') {
    // parse a file upload
    var form = new formidable.IncomingForm();
    form.parse(req, function(err, fields, files) {
      res.writeHead(200, {'content-type': 'text/plain'});
      res.write('received upload:\n\n');
      res.end(util.inspect({fields: fields, files: files}));
  // show a file upload form
  res.writeHead(200, {'content-type': 'text/html'});
    '<form action="/upload" enctype="multipart/form-data" method="post">'+
    '<input type="text" name="title"><br>'+
    '<input type="file" name="upload" multiple="multiple"><br>'+
    '<input type="submit" value="Upload">'+



var form = new formidable.IncomingForm()

Creates a new incoming form.

form.encoding = 'utf-8';

Sets encoding for incoming form fields.

form.uploadDir = "/my/dir";

Sets the directory for placing file uploads in. You can move them later on using fs.rename(). The default is os.tmpdir().

form.keepExtensions = false;

If you want the files written to form.uploadDir to include the extensions of the original files, set this property to true.


Either 'multipart' or 'urlencoded' depending on the incoming request.

form.maxFieldsSize = 2 * 1024 * 1024;

Limits the amount of memory all fields together (except files) can allocate in bytes. If this value is exceeded, an 'error' event is emitted. The default size is 2MB.

form.maxFields = 1000;

Limits the number of fields that the querystring parser will decode. Defaults to 1000 (0 for unlimited).

form.hash = false;

If you want checksums calculated for incoming files, set this to either 'sha1' or 'md5'.

form.multiples = false;

If this option is enabled, when you call form.parse, the files argument will contain arrays of files for inputs which submit multiple files using the HTML5 multiple attribute.


The amount of bytes received for this form so far.


The expected number of bytes in this form.

form.parse(request, [cb]);

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

form.parse(req, function(err, fields, 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.

form.onPart = function(part) {
  part.addListener('data', function() {
    // ...

If you want to use formidable to only handle certain parts for you, you can do so:

form.onPart = function(part) {
  if (!part.filename) {
    // let formidable handle all non-file parts

Check the code in this method for further inspiration.


file.size = 0

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.path = null

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. = null

The name this file had according to the uploading client.

file.type = null

The mime type of this file, according to the uploading client.

file.lastModifiedDate = 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.hash = null

If hash calculation was set, you can read the hex digest out of this var.


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', function(bytesReceived, bytesExpected) {


Emitted whenever a field / value pair has been received.

form.on('field', function(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', function(name, file) {


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

form.on('file', function(name, file) {


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.

form.on('error', function(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', function() {
form.on('end', function() {

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.



  • add support to Node.JS 7


  • Add failing hash tests. (Ben Trask)
  • Enable hash calculation again (Eugene Girshov)
  • Test for immediate data events (Tim Smart)
  • Re-arrange IncomingForm#parse (Tim Smart)


  • Only update hash if update method exists (Sven Lito)
  • According to travis v0.10 needs to go quoted (Sven Lito)
  • Bumping build node versions (Sven Lito)
  • Additional fix for empty requests (Eugene Girshov)
  • Change the default to 1000, to match the new Node behaviour. (OrangeDog)
  • Add ability to control maxKeys in the querystring parser. (OrangeDog)
  • Adjust test case to work with node 0.9.x (Eugene Girshov)
  • Update package.json (Sven Lito)
  • Path adjustment according to eb4468b (Markus Ast)


  • Emit error on aborted connections (Eugene Girshov)
  • Add support for empty requests (Eugene Girshov)
  • Fix name/filename handling in Content-Disposition (jesperp)
  • Tolerate malformed closing boundary in multipart (Eugene Girshov)
  • Ignore preamble in multipart messages (Eugene Girshov)
  • Add support for application/json (Mike Frey, Carlos Rodriguez)
  • Add support for Base64 encoding (Elmer Bulthuis)
  • Add File#toJSON (TJ Holowaychuk)
  • Remove support for Node.js 0.4 & 0.6 (Andrew Kelley)
  • Documentation improvements (Sven Lito, Andre Azevedo)
  • Add support for application/octet-stream (Ion Lupascu, Chris Scribner)
  • Use os.tmpdir() to get tmp directory (Andrew Kelley)
  • Improve package.json (Andrew Kelley, Sven Lito)
  • Fix benchmark script (Andrew Kelley)
  • Fix scope issue in incoming_forms (Sven Lito)
  • Fix file handle leak on error (OrangeDog)


  • Calculate checksums for incoming files (sreuter)
  • Add definition parameters to "IncomingForm" as an argument (Math-)


  • Make parts to be proper Streams (Matt Robenolt)


  • Emit progress when content length header parsed (Tim Koschützki)
  • Fix Readme syntax due to GitHub changes (goob)
  • Replace references to old 'sys' module in Readme with 'util' (Peter Sugihara)


  • Strip potentially unsafe characters when using keepExtensions: true.
  • Switch to utest / urun for testing
  • Add travis build


  • Remove file from package that was causing problems when installing on windows. (#102)
  • Fix typos in Readme (Jason Davies).


  • Do not default to the default to the field name for file uploads where filename="".


  • Support filename="" in multipart parts
  • Explain unexpected end() errors in parser better

Note: Starting with this version, formidable emits 'file' events for empty file input fields. Previously those were incorrectly emitted as regular file input fields with value = "".


  • Detect a good default tmp directory regardless of platform. (#88)


  • Fix problems with utf8 characters (#84) / semicolons in filenames (#58)
  • Small performance improvements
  • New test suite and fixture system


  • Exclude node_modules folder from git
  • Implement new 'aborted' event
  • Fix files in example folder to work with recent node versions
  • Make gently a devDependency

See Commits


  • Fix package.json to refer to proper main directory. (#68, Dean Landolt)

See Commits


  • Add support for multipart boundaries that are quoted strings. (Jeff Craig)

This marks the beginning of development on version 2.0 which will include several architectural improvements.

See Commits


  • Emit 'progress' event when receiving data, regardless of parsing it. (Tim Koschützki)
  • Use W3C FileAPI Draft properties for File class

Important: The old property names of the File class will be removed in a future release.

See Commits

Older releases

These releases were done before starting to maintain the above Changelog:


Formidable is licensed under the MIT license.






npm i st-formidable

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