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A library to create readable "multipart/form-data" streams. Can be used to submit forms and file uploads to other web applications.


Version published
Weekly downloads
increased by1.36%

Weekly downloads



  • Merge pull request #382 from wxt2005/custom-stream 8968e01
  • Fix typo e705c0a
  • Merge branch 'master' of into custom-stream b7b7dee
  • Update README for custom stream behavior 6dd8624
  • Handle custom stream a3e191d



Form-Data NPM Module Join the chat at

A library to create readable "multipart/form-data" streams. Can be used to submit forms and file uploads to other web applications.

The API of this library is inspired by the XMLHttpRequest-2 FormData Interface.

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npm install --save form-data


In this example we are constructing a form with 3 fields that contain a string, a buffer and a file stream.

var FormData = require('form-data'); var fs = require('fs'); var form = new FormData(); form.append('my_field', 'my value'); form.append('my_buffer', new Buffer(10)); form.append('my_file', fs.createReadStream('/foo/bar.jpg'));

Also you can use http-response stream:

var FormData = require('form-data'); var http = require('http'); var form = new FormData(); http.request('', function(response) { form.append('my_field', 'my value'); form.append('my_buffer', new Buffer(10)); form.append('my_logo', response); });

Or @mikeal's request stream:

var FormData = require('form-data'); var request = require('request'); var form = new FormData(); form.append('my_field', 'my value'); form.append('my_buffer', new Buffer(10)); form.append('my_logo', request(''));

In order to submit this form to a web application, call submit(url, [callback]) method:

form.submit('', function(err, res) { // res – response object (http.IncomingMessage) // res.resume(); });

For more advanced request manipulations submit() method returns http.ClientRequest object, or you can choose from one of the alternative submission methods.

Custom options

You can provide custom options, such as maxDataSize:

var FormData = require('form-data'); var form = new FormData({ maxDataSize: 20971520 }); form.append('my_field', 'my value'); form.append('my_buffer', /* something big */);

List of available options could be found in combined-stream

Alternative submission methods

You can use node's http client interface:

var http = require('http'); var request = http.request({ method: 'post', host: '', path: '/upload', headers: form.getHeaders() }); form.pipe(request); request.on('response', function(res) { console.log(res.statusCode); });

Or if you would prefer the 'Content-Length' header to be set for you:

form.submit('', function(err, res) { console.log(res.statusCode); });

To use custom headers and pre-known length in parts:

var CRLF = '\r\n'; var form = new FormData(); var options = { header: CRLF + '--' + form.getBoundary() + CRLF + 'X-Custom-Header: 123' + CRLF + CRLF, knownLength: 1 }; form.append('my_buffer', buffer, options); form.submit('', function(err, res) { if (err) throw err; console.log('Done'); });

Form-Data can recognize and fetch all the required information from common types of streams (fs.readStream, http.response and mikeal's request), for some other types of streams you'd need to provide "file"-related information manually:, stdout, stderr) { if (err) throw err; var form = new FormData(); form.append('file', stdout, { filename: 'unicycle.jpg', // ... or: filepath: 'photos/toys/unicycle.jpg', contentType: 'image/jpeg', knownLength: 19806 }); form.submit('', function(err, res) { if (err) throw err; console.log('Done'); }); });

The filepath property overrides filename and may contain a relative path. This is typically used when uploading multiple files from a directory.

For edge cases, like POST request to URL with query string or to pass HTTP auth credentials, object can be passed to form.submit() as first parameter:

form.submit({ host: '', path: '/probably.php?extra=params', auth: 'username:password' }, function(err, res) { console.log(res.statusCode); });

In case you need to also send custom HTTP headers with the POST request, you can use the headers key in first parameter of form.submit():

form.submit({ host: '', path: '/surelynot.php', headers: {'x-test-header': 'test-header-value'} }, function(err, res) { console.log(res.statusCode); });


Void append( String field, Mixed value [, Mixed options] )

Append data to the form. You can submit about any format (string, integer, boolean, buffer, etc.). However, Arrays are not supported and need to be turned into strings by the user.

var form = new FormData(); form.append( 'my_string', 'my value' ); form.append( 'my_integer', 1 ); form.append( 'my_boolean', true ); form.append( 'my_buffer', new Buffer(10) ); form.append( 'my_array_as_json', JSON.stringify( ['bird','cute'] ) )

You may provide a string for options, or an object.

// Set filename by providing a string for options form.append( 'my_file', fs.createReadStream('/foo/bar.jpg'), 'bar.jpg' ); // provide an object. form.append( 'my_file', fs.createReadStream('/foo/bar.jpg'), {filename: 'bar.jpg', contentType: 'image/jpeg', knownLength: 19806} );
Headers getHeaders( [Headers userHeaders] )

This method adds the correct content-type header to the provided array of userHeaders.

String getBoundary()

Return the boundary of the formData. By default, the boundary consists of 26 - followed by 24 numbers for example:

Void setBoundary(String boundary)

Set the boundary string, overriding the default behavior described above.

Note: The boundary must be unique and may not appear in the data.

Buffer getBuffer()

Return the full formdata request package, as a Buffer. You can insert this Buffer in e.g. Axios to send multipart data.

var form = new FormData(); form.append( 'my_buffer', Buffer.from([0x4a,0x42,0x20,0x52,0x6f,0x63,0x6b,0x73]) ); form.append( 'my_file', fs.readFileSync('/foo/bar.jpg') ); '', form.getBuffer(), form.getHeaders() )

Note: Because the output is of type Buffer, you can only append types that are accepted by Buffer: string, Buffer, ArrayBuffer, Array, or Array-like Object. A ReadStream for example will result in an error.

Integer getLengthSync()

Same as getLength but synchronous.

Note: getLengthSync doesn't calculate streams length.

Integer getLength( function callback )

Returns the Content-Length async. The callback is used to handle errors and continue once the length has been calculated

this.getLength(function(err, length) { if (err) { this._error(err); return; } // add content length request.setHeader('Content-Length', length); ... }.bind(this));
Boolean hasKnownLength()

Checks if the length of added values is known.

Request submit( params, function callback )

Submit the form to a web application.

var form = new FormData(); form.append( 'my_string', 'Hello World' ); form.submit( '', function(err, res) { // res – response object (http.IncomingMessage) // res.resume(); } );
String toString()

Returns the form data as a string. Don't use this if you are sending files or buffers, use getBuffer() instead.

Integration with other libraries


Form submission using request:

var formData = { my_field: 'my_value', my_file: fs.createReadStream(__dirname + '/unicycle.jpg'), };{url:'', formData: formData}, function(err, httpResponse, body) { if (err) { return console.error('upload failed:', err); } console.log('Upload successful! Server responded with:', body); });

For more details see request readme.


You can also submit a form using node-fetch:

var form = new FormData(); form.append('a', 1); fetch('', { method: 'POST', body: form }) .then(function(res) { return res.json(); }).then(function(json) { console.log(json); });

In Node.js you can post a file using axios:

const form = new FormData(); const stream = fs.createReadStream(PATH_TO_FILE); form.append('image', stream); // In Node.js environment you need to set boundary in the header field 'Content-Type' by calling method `getHeaders` const formHeaders = form.getHeaders();'', form, { headers: { ...formHeaders, }, }) .then(response => response) .catch(error => error)


  • getLengthSync() method DOESN'T calculate length for streams, use knownLength options as workaround.
  • getLength(cb) will send an error as first parameter of callback if stream length cannot be calculated (e.g. send in custom streams w/o using knownLength).
  • submit will not add content-length if form length is unknown or not calculable.
  • Starting version 2.x FormData has dropped support for [email protected].
  • Starting version 3.x FormData has dropped support for [email protected].


Form-Data is released under the MIT license.


What is form-data?

A library to create readable "multipart/form-data" streams. Can be used to submit forms and file uploads to other web applications.

Is form-data popular?

The npm package form-data receives a total of 44,667,516 weekly downloads. As such, form-data popularity was classified as popular.

Is form-data well maintained?

We found that form-data demonstrated a not healthy version release cadence and project activity. It has 4 open source maintainers collaborating on the project.

Last updated on 15 Feb 2021


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