FormData

FormData implementation for Node.js

Installation

You can install this package with npm:

npm install formdata-node

Or yarn:

yarn add formdata-node

Or pnpm

pnpm add formdata-node

Usage

This package has its own encoder that allows to read the content from the FormData instances into the multipart/form-data format. Just use Symbol.asyncIterator method to get async iterator or just access FormData#stream property to get Readable stream. Note that in the next major release both of this methods will be removed in favour of form-data-encoder, which is basically the reimplementation of builtin formdata-node encoder that was separated from this package to allow to re-use it in different HTTP clients or use it to add some additional logic into the encoding process. See form-data-encoder documentation to get more information.

1. Let's take a look at minimal example with got:

import {FormData} from "formdata-node"

import got from "got"

const fd = new FormData()

fd.set("greeting", "Hello, World!")

const options = {
  body: fd.stream, // Set internal stream as request body
  headers: fd.headers // Set headers of the current FormData instance
}

got.post("https://httpbin.org/post", options)
  .then(res => console.log("Res: ", res.body))
  .catch(err => console.error("Error: ", err))

2. Because every FormData instance (in this package) has Symbol.asyncIterator method, you can create a stream from it using Readable.from():

import {Readable} from "stream"

import {FormData} from "formdata-node"

import fetch from "node-fetch"

const fd = new FormData()

fd.set("field", "Some value")

const options = {
  method: "post",
  headers: fd.headers,
  body: Readable.from(fd)
}

await fetch("https://httpbin.org/post", options)

4. Encode entries using form-data-encoder (in cases when HTTP client does not support spec-compatible FormData):

import {Readable} from "stream"

import {Encoder} from "form-data-encoder"
import {FormData} from "formdata-node"

import fetch from "node-fetch"

const fd = new FormData()

fd.set("field", "Some value")

const encoder = new Encoder(fd)

const options = {
  method: "post",
  headers: encoder.headers,
  body: Readable.from(encoder)
}

await fetch("https://httpbin.org/post", options)

4. Sending files over form-data:

import {createReadStream} from "fs"

import {FormData} from "formdata-node"

// I assume that there's node-fetch@3 is used for this example since it has formdata-node support out of the box
// Note that they still in beta.
import fetch from "node-fetch"

const fd = new FormData()

fd.set("file", createReadStream("/path/to/a/file"))

// Just like that, you can send a file with formdata-node
await fetch("https://httpbin.org/post", {method: "post", body: fd})

5. You can also append files using fileFromPath or fileFromPathSync helpers. It does the same thing as fetch-blob/from, but returns a File instead of Blob:

import {FormData, fileFromPath} from "formdata-node"

import fetch from "node-fetch"

const fd = new FormData()

fd.set("file", await fileFromPath("/path/to/a/file"))

await fetch("https://httpbin.org/post", {method: "post", body: fd})

Note that this method is preferable over the fs.createReadStream() and will be the only option (along with its async version) in next major release.

6. And of course you can create your own File manually – formdata-node gets you covered. It has a File object that inherits Blob from fetch-blob package:

import {FormData, File} from "formdata-node"

import fetch from "node-fetch"

const fd = new FormData()
const file = new File(["My hovercraft is full of eels"], "hovercraft.txt")

fd.set("file", file)

await fetch("https://httpbin.org/post", {method: "post", body: fd})

7. Blobs as field's values allowed too:

import {FormData} from "formdata-node"

import Blob from "fetch-blob"

const fd = new FormData()
const blob = new Blob(["Some content"], {type: "text/plain"})

fd.set("blob", blob)

// Will always be returned as `File`
let file = fd.get("blob")

// The created file has "blob" as the name by default
console.log(file.name) // -> blob

// To change that, you need to set filename argument manually
fd.set("file", blob, "some-file.txt")

file = fd.get("file")

console.log(file.name) // -> some-file.txt

8. You can still use files sourced from any stream, but unlike in v2 you'll need some extra work to achieve that:

import {Readable} from "stream"

import {FormData} from "formdata-node"

class BlobFromStream {
  #stream

  constructor(stream, size) {
    this.#stream = stream
    this.size = size
  }

  stream() {
    return this.#stream
  }

  get [Symbol.toStringTag]() {
    return "Blob"
  }
}

const content = Buffer.from("Stream content")

const stream = new Readable({
  read() {
    this.push(content)
    this.push(null)
  }
})

const fd = new FormData()

fd.set("stream", new BlobFromStream(stream, content.length), "file.txt")

await fetch("https://httpbin.org/post", {method: "post", body: fd})

9. Note that if you don't know the length of that stream, you'll also need to handle form-data encoding manually or use form-data-encoder package. This is necessary to control which headers will be sent with your HTTP request:

import {Readable} from "stream"

import {Encoder} from "form-data-encoder"
import {FormData} from "formdata-node"

const fd = new FormData()

// You can use file-shaped or blob-shaped objects as FormData value instead of creating separate class
fd.set("stream", {
  type: "text/plain",
  name: "file.txt",
  [Symbol.toStringTag]: "File",
  stream() {
    return getStreamFromSomewhere()
  }
})

const encoder = new Encoder(fd)

const options = {
  method: "post",
  headers: {
    "content-type": encoder.contentType
  },
  body: Readable.from(encoder)
}

await fetch("https://httpbin.org/post", {method: "post", body: fd})

API

class FormData

constructor([entries]) -> {FormData}

Creates a new FormData instance

• {array} [entries = null] – an optional FormData initial entries. Each initial field should be passed as a collection of the objects with "name", "value" and "filename" props. See the FormData#append() for more info about the available format.

Instance properties

boundary -> {string}

Returns a boundary string of the current FormData instance. Read-only property.

stream -> {stream.Readable}

Deprecated! This property will be removed in 4.x version. Use form-data-encoder to encode FormData into multipart/form-data format in case if your HTTP client does not support spec-compatible FormData implementations.

Returns an internal Readable stream. Use it to send queries, but don't push anything into it. Read-only property.

headers -> {object}

Deprecated! This property will be removed in 4.x version. Use form-data-encoder to encode FormData into multipart/form-data format in case if your HTTP client does not support spec-compatible FormData implementations.

Returns object with Content-Type header. Read-only property.

Instance methods

set(name, value[, filename, options]) -> {void}

Set a new value for an existing key inside FormData, or add the new field if it does not already exist.

• {string} name – The name of the field whose data is contained in value
• {unknown} value – The field value. You can pass any JavaScript primitive type (including null and undefined), Buffer, ReadStream, Blob or File. Note that Arrays and Object will be converted to string by using String function.
• {string} [filename = undefined] – A filename of given field. Can be added only for Buffer, File, Blob and ReadStream. You can set it either from and argument or options.
• {object} [object = {}] - Additional field options
• {string} [object.filename = undefined] – A filename of given field. Can be added only for Buffer, File, Blob and ReadStream. You can set it either from and argument or options.
• {number} [options.lastModified = Date.now()] – provides the last modified date of the file as the number of milliseconds since the Unix epoch (January 1, 1970 at midnight). Files without a known last modified date return the current date.
• {string} [options.type = ""] - Returns the media type (MIME) of the file represented by a File object.

append(name, value[, filename, options]) -> {void}

Appends a new value onto an existing key inside a FormData object, or adds the key if it does not already exist.

• {string} name – The name of the field whose data is contained in value
• {unknown} value – The field value. You can pass any JavaScript primitive type (including null and undefined), Buffer, ReadStream, Blob or File. Note that Arrays and Object will be converted to string by using String function.
• {string} [filename = undefined] – A filename of given field. Can be added only for Buffer, File, Blob and ReadStream. You can set it either from and argument or options.
• {object} [object = {}] - Additional field options
• {string} [object.filename = undefined] – A filename of given field. Can be added only for Buffer, File, Blob and ReadStream. You can set it either from and argument or options.
• {number} [options.lastModified = Date.now()] – provides the last modified date of the file as the number of milliseconds since the Unix epoch (January 1, 1970 at midnight). Files without a known last modified date return the current date.
• {string} [options.type = ""] - Returns the media type (MIME) of the file represented by a File object.

get(name) -> {string | File}

Returns the first value associated with the given name. If the field has Blob, Buffer, File or ReadStream value, the File-like object will be returned.

• {string} name – A name of the value you want to retrieve.

getAll(name) -> {Array<string | File>}

Returns all the values associated with a given key from within a FormData object. If the field has Blob, Buffer, File or ReadStream value, the File-like object will be returned.

• {string} name – A name of the value you want to retrieve.

has(name) -> {boolean}

Check if a field with the given name exists inside FormData.

• {string} – A name of the field you want to test for.

delete(name) -> {void}

Deletes a key and its value(s) from a FormData object.

• {string} name – The name of the key you want to delete.

getComputedLength() -> {number}

Deprecated! This property will be removed in 4.x version. Use form-data-encoder to encode FormData into multipart/form-data format in case if your HTTP client does not support spec-compatible FormData implementations.

Returns computed length of the FormData content.

forEach(callback[, ctx]) -> {void}

Executes a given callback for each field of the FormData instance

• {function} callback – Function to execute for each element, taking three arguments:
  • {string | File} value – A value(s) of the current field.
  • {string} name – Name of the current field.
  • {FormData} fd – The FormData instance that forEach is being applied to
• {unknown} [ctx = null] – Value to use as this context when executing the given callback

keys() -> {Generator<string>}

Returns an iterator allowing to go through the FormData keys

values() -> {Generator<string | File>}

Returns an iterator allowing to go through the FormData values

entries() -> {Generator<[string, string | File]>}

Returns an iterator allowing to go through the FormData key/value pairs

[Symbol.iterator]() -> {Generator<[string, string | File]>}

An alias for FormData#entries()

[Symbol.asyncIterator]() -> {AsyncGenerator<Buffer>}

Deprecated! This property will be removed in 4.x version. Use form-data-encoder to encode FormData into multipart/form-data format in case if your HTTP client does not support spec-compatible FormData implementations.

Returns an async iterator allowing to read form-data body using for-await-of syntax. Read the async iteration proposal to get more info about async iterators.

class File extends Blob

constructor(blobParts, filename[, options]) -> {File}

The File class provides information about files. The File object inherits Blob from fetch-blob package.

• {(ArrayBufferLike | ArrayBufferView | Blob | Buffer | string)[]} blobParts
• {string} filename – Representing the file name.
• {object} [options = {}] - An options object containing optional attributes for the file. Available options are as follows
• {number} [options.lastModified = Date.now()] – provides the last modified date of the file as the number of milliseconds since the Unix epoch (January 1, 1970 at midnight). Files without a known last modified date return the current date.
• {string} [options.type = ""] - Returns the media type (MIME) of the file represented by a File object.

fileFromPath(path[, filename, options]) -> {Promise<File>}

Creates a File referencing the one on a disk by given path.

• {string} path - Path to a file
• {string} [filename] - Name of the file. Will be passed as second argument in File constructor. If not presented, the file path will be used to get it.
• {object} [options = {}] - File options.
• {string} [options.type = ""] - Returns the media type (MIME) of the file represented by a File object.

fileFromPathSync(path[, filename, options]) -> {File}

Creates a File referencing the one on a disk by given path. Synchronous version of the fileFromPath.

• {string} path - Path to a file
• {string} [filename] - Name of the file. Will be passed as second argument in File constructor. If not presented, the file path will be used to get it.
• {object} [options = {}] - File options.
• {string} [options.type = ""] - Returns the media type (MIME) of the file represented by a File object.

isFileLike(value) -> {boolean}

Check if given value is a File, Blob or file-look-a-like object.

• {unknown} value - A value to test

Related links

• FormData documentation on MDN
• File documentation on MDN
• Blob documentation on MDN
• formdata-polyfill HTML5 FormData for Browsers & NodeJS.
• fetch-blob a Blob implementation on node.js, originally from node-fetch.
• form-data-encoder - Encoder for multipart/form-data
• then-busboy a promise-based wrapper around Busboy. Process multipart/form-data content and returns it as a single object. Will be helpful to handle your data on the server-side applications.
• @octetstream/object-to-form-data converts JavaScript object to FormData.