form-data

What is form-data?

The form-data npm package is used to create `multipart/form-data` streams that can be used to perform HTTP requests with file uploads and other form data. It is commonly used with request libraries to submit forms and upload files to a server.

What are form-data's main functionalities?

Appending fields

This feature allows you to append key-value pairs to the form-data object, which can represent text fields in a form.

const FormData = require('form-data');
const form = new FormData();
form.append('username', 'exampleUser');
form.append('password', 'examplePassword');

Appending files

This feature allows you to append files to the form-data object, which can be used to upload files to a server.

const FormData = require('form-data');
const fs = require('fs');
const form = new FormData();
form.append('file', fs.createReadStream('/path/to/file.txt'), 'file.txt');

Custom headers

This feature allows you to retrieve custom headers required for submitting the form-data object, including the correct `Content-Type` header with the boundary.

const FormData = require('form-data');
const form = new FormData();
const customHeaders = form.getHeaders({'custom-header': 'value'});
// customHeaders can now be used with an HTTP client to send the form with custom headers.

Piping to a HTTP request

This feature demonstrates how to pipe the form-data directly to an HTTP request, which is useful for uploading files and submitting forms.

const FormData = require('form-data');
const http = require('http');
const form = new FormData();
form.append('field', 'value');

const request = http.request({
  method: 'post',
  host: 'example.com',
  path: '/upload',
  headers: form.getHeaders()
});

form.pipe(request);

Other packages similar to form-data

busboy

Busboy is a Node.js module for parsing incoming HTML form data. It is particularly good at handling file uploads, but unlike form-data, it is used on the server side to parse incoming requests.

multiparty

Multiparty is an npm package for parsing `multipart/form-data` requests, similar to busboy. It is also used on the server side and provides an alternative to form-data for handling file uploads and multipart form data.

multer

Multer is a Node.js middleware for handling `multipart/form-data`, which is primarily used for uploading files. It is designed for use with Express and is often preferred for its ease of integration with Express applications, compared to form-data which is more general-purpose.

README

form-data

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

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

Install

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Usage

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('http://nodejs.org/images/logo.png', 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('http://nodejs.org/images/logo.png'));

In order to submit this form to a web application, you can use node's http client interface:

var http = require('http');

var request = http.request({
  method: 'post',
  host: 'example.org',
  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('example.org/upload', 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('http://example.com/', function(err, res) {
  if (err) throw err;
  console.log('Done');
});

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

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