FormData
Spec-compliant FormData
implementation for Node.js
Requirements
For this module to work consider polyfilling: ReadableStream, and DOMException (if you use file-from-path
utilities)
Highlights
- Spec-compliant: implements every method of the
FormData interface
. - Supports Blobs and Files sourced from anywhere: you can use builtin
fileFromPath
andfileFromPathSync
helpers to create a File from FS, or you can implement yourBlobDataItem
object to use a different source of data. - Written on TypeScript and ships with TS typings.
- Isomorphic, but only re-exports native FormData object for browsers. If you need a polyfill for browsers, use
formdata-polyfill
- It's a
ponyfill
! Which means, no effect has been caused onglobalThis
or nativeFormData
implementation.
Blob/File support
While formdata-node
ships with its own File
and Blob
implementations, these might eventually be removed in favour of Node.js' Blob
(introduced in v14.18) and File (when it will be introduced). In order to help you smoothen that transition period, our own Blob
and File
, as well as FormData
itself, provides support Blob
objects created by Node.js' implementation.
Installation
You can install this package with npm:
npm install formdata-node
Or yarn:
yarn add formdata-node
Or pnpm
pnpm add formdata-node
ESM/CJS support
This package is build for and bundled for both ESM and CommonJS, so you can use it in both environments.
Usage
- Let's take a look at minimal example with got:
import {FormData} from "formdata-node"
// I assume Got >= 12.x is used for this example
import got from "got"
const form = new FormData()
form.set("greeting", "Hello, World!")
const data = await got.post("https://httpbin.org/post", {body: form}).json()
console.log(data.form.greeting) // => Hello, World!
- If your HTTP client does not support spec-compliant FormData, you can use
form-data-encoder
to encode entries:
import {Readable} from "stream"
import {FormDataEncoder} from "form-data-encoder"
import {FormData} from "formdata-node"
// Note that `node-fetch` >= 3.x have builtin support for spec-compliant FormData, sou you'll only need the `form-data-encoder` if you use `node-fetch` <= 2.x.
import fetch from "node-fetch"
const form = new FormData()
form.set("field", "Some value")
const encoder = new FormDataEncoder(form)
const options = {
method: "post",
headers: encoder.headers,
body: Readable.from(encoder)
}
await fetch("https://httpbin.org/post", options)
- Sending files over form-data:
import {FormData, File} from "formdata-node" // You can use `File` from fetch-blob >= 3.x
import fetch from "node-fetch"
const form = new FormData()
const file = new File(["My hovercraft is full of eels"], "file.txt")
form.set("file", file)
await fetch("https://httpbin.org/post", {method: "post", body: form})
- Blobs as field's values allowed too:
import {FormData, Blob} from "formdata-node" // You can use `Blob` from fetch-blob
const form = new FormData()
const blob = new Blob(["Some content"], {type: "text/plain"})
form.set("blob", blob)
// Will always be returned as `File`
let file = form.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
form.set("file", blob, "some-file.txt")
file = form.get("file")
console.log(file.name) // -> some-file.txt
- You can use 3rd party Blob as FormData value, as vell as for BlobParts in out Blob implementation:
import {FormData, Blob} from "formdata-node"
import {Blob as FetchBlob} from "fetch-blob"
const input = new FetchBlob(["a", "b", "c"])
const blob = new Blob([input]) // Accepts 3rd party blobs as BlobParts
await blob.text() // -> abc
const form = new FormData()
form.set("file", input)
const file = form.get("file") // -> File
await file.text() // -> abc
- You can also use Node.js' Blob implementation in these scenarios:
import {Blob as NodeBlob} from "node:buffer"
import {FormData, Blob} from "formdata-node"
const input = new NodeBlob(["a", "b", "c"])
const blob = new Blob([input]) // Accepts Node.js' Blob implementation as BlobParts
await blob.text() // -> abc
const form = new FormData()
form.set("file", input)
const file = form.get("file") // -> File
await file.text() // -> abc
- You can also append files using
fileFromPath
orfileFromPathSync
helpers. It does the same thing asfetch-blob/from
, but returns aFile
instead ofBlob
:
import {fileFromPath} from "formdata-node/file-from-path"
import {FormData} from "formdata-node"
import fetch from "node-fetch"
const form = new FormData()
form.set("file", await fileFromPath("/path/to/a/file"))
await fetch("https://httpbin.org/post", {method: "post", body: form})
- 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 form = new FormData()
form.set("stream", new BlobFromStream(stream, content.length), "file.txt")
await fetch("https://httpbin.org/post", {method: "post", body: form})
- 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 form = new FormData()
// You can use file-shaped or blob-shaped objects as FormData value instead of creating separate class
form.set("stream", {
type: "text/plain",
name: "file.txt",
[Symbol.toStringTag]: "File",
stream() {
return getStreamFromSomewhere()
}
})
const encoder = new Encoder(form)
const options = {
method: "post",
headers: {
"content-type": encoder.contentType
},
body: Readable.from(encoder)
}
await fetch("https://httpbin.org/post", {method: "post", body: form})
Comparison
formdata-node | formdata-polyfill | undici FormData | form-data | |
---|---|---|---|---|
.append() | ✔️ | ✔️ | ✔️ | ✔️1 |
.set() | ✔️ | ✔️ | ✔️ | ❌ |
.get() | ✔️ | ✔️ | ✔️ | ❌ |
.getAll() | ✔️ | ✔️ | ✔️ | ❌ |
.forEach() | ✔️ | ✔️ | ✔️ | ❌ |
.keys() | ✔️ | ✔️ | ✔️ | ❌ |
.values() | ✔️ | ✔️ | ✔️ | ❌ |
.entries() | ✔️ | ✔️ | ✔️ | ❌ |
Symbol.iterator | ✔️ | ✔️ | ✔️ | ❌ |
ESM | ✔️ | ✔️ | ✔️2 | ✔️2 |
Blob | ✔️3 | ✔️4 | ✔️3 | ❌ |
Browser polyfill | ❌ | ✔️ | ✔️ | ❌ |
Builtin encoder | ❌ | ✔️ | ✔️5 | ✔️ |
1 Does not support Blob and File in entry value, but allows streams and Buffer (which is not spec-compliant, however).
2 Can be imported in ESM, because Node.js support for CJS modules in ESM context, but it does not have ESM entry point.
3 Have builtin implementations of Blob and/or File, allows native Blob and File as entry value.
4 Support Blob and File via fetch-blob package, allows native Blob and File as entry value.
5 Have multipart/form-data
encoder as part of their fetch
implementation.
✔️ - For FormData methods, indicates that the method is present and spec-compliant. For features, shows its presence.
❌ - Indicates that method or feature is not implemented.
API
class FormData
constructor() -> {FormData}
Creates a new FormData instance.
Instance methods
set(name, value[, filename]) -> {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's value. This can be
Blob
orFile
. If none of these are specified the value is converted to a string. - {string} [filename = undefined] – The filename reported to the server, when a Blob or File is passed as the second parameter. The default filename for Blob objects is "blob". The default filename for File objects is the file's filename.
append(name, value[, filename]) -> {void}
Appends a new value onto an existing key inside a FormData object, or adds the key if it does not already exist.
The difference between set()
and append()
is that if the specified key already exists, set()
will overwrite all existing values with the new one, whereas append()
will append the new value onto the end of the existing set of values.
-
{string} name – The name of the field whose data is contained in
value
. -
{unknown} value – The field's value. This can be
Blob
orFile
. If none of these are specified the value is converted to a string. - {string} [filename = undefined] – The filename reported to the server, when a Blob or File is passed as the second parameter. The default filename for Blob objects is "blob". The default filename for File objects is the file's filename.
get(name) -> {FormDataValue}
Returns the first value associated with a given key from within a FormData
object.
If you expect multiple values and want all of them, use the getAll()
method instead.
- {string} name – A name of the value you want to retrieve.
getAll(name) -> {Array<FormDataValue>}
Returns all the values associated with a given key from within a FormData
object.
- {string} name – A name of the value you want to retrieve.
has(name) -> {boolean}
Returns a boolean stating whether a FormData
object contains a certain key.
- {string} – A string representing the name of the key 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.
forEach(callback[, thisArg]) -> {void}
Executes a given callback for each field of the FormData instance
-
{function} callback – Function to execute for each element, taking three arguments:
- {FormDataValue} value – A value(s) of the current field.
- {string} name – Name of the current field.
- {FormData} form – The FormData instance that forEach is being applied to
- {unknown} [thisArg = null] – Value to use as this context when executing the given callback
keys() -> {Generator<string>}
Returns an iterator
allowing to go through all keys contained in this FormData
object.
Each key is a string
.
values() -> {Generator<FormDataValue>}
Returns an iterator
allowing to go through all values contained in this object FormData
object.
Each value is a FormDataValue
.
entries() -> {Generator<[string, FormDataValue]>}
Returns an iterator
allowing to go through key/value pairs contained in this FormData
object.
The key of each pair is a string; the value is a FormDataValue
.
[Symbol.iterator]() -> {Generator<[string, FormDataValue]>}
An alias for FormData#entries()
class Blob
The Blob
object represents a blob, which is a file-like object of immutable, raw data;
they can be read as text or binary data, or converted into a ReadableStream
so its methods can be used for processing the data.
constructor(blobParts[, options]) -> {Blob}
Creates a new Blob
instance. The Blob
constructor accepts following arguments:
-
{(ArrayBufferLike | ArrayBufferView | File | Blob | string)[]} blobParts – An
Array
strings, orArrayBuffer
,ArrayBufferView
,Blob
objects, or a mix of any of such objects, that will be put inside theBlob
; - {object} [options = {}] - An options object containing optional attributes for the file. Available options are as follows;
-
{string} [options.type = ""] - Returns the media type (
MIME
) of the blob represented by aBlob
object.
Instance properties
type -> {string}
Returns the MIME type
of the Blob
or File
.
size -> {number}
Returns the size of the Blob
or File
in bytes.
Instance methods
slice([start, end, contentType]) -> {Blob}
Creates and returns a new Blob
object which contains data from a subset of the blob on which it's called.
-
{number} [start = 0] An index into the
Blob
indicating the first byte to include in the newBlob
. If you specify a negative value, it's treated as an offset from the end of theBlob
toward the beginning. For example, -10 would be the 10th from last byte in theBlob
. The default value is 0. If you specify a value for start that is larger than the size of the sourceBlob
, the returnedBlob
has size 0 and contains no data. -
{number} [end =
blob
.size] An index into theBlob
indicating the first byte that will not be included in the newBlob
(i.e. the byte exactly at this index is not included). If you specify a negative value, it's treated as an offset from the end of theBlob
toward the beginning. For example, -10 would be the 10th from last byte in theBlob
. The default value is size. -
{string} [contentType = ""] The content type to assign to the new
Blob
; this will be the value of its type property. The default value is an empty string.
stream() -> {ReadableStream<Uint8Array>}
Returns a ReadableStream
which upon reading returns the data contained within the Blob
.
arrayBuffer() -> {Promise<ArrayBuffer>}
Returns a Promise
that resolves with the contents of the blob as binary data contained in an ArrayBuffer
.
text() -> {Promise<string>}
Returns a Promise
that resolves with a string containing the contents of the blob, interpreted as UTF-8.
class File extends Blob
The File
class provides information about files. The File
class inherits Blob
.
constructor(fileBits, filename[, options]) -> {File}
Creates a new File
instance. The File
constructor accepts following arguments:
-
{(ArrayBufferLike | ArrayBufferView | File | Blob | string)[]} fileBits – An
Array
strings, orArrayBuffer
,ArrayBufferView
,Blob
objects, or a mix of any of such objects, that will be put inside theFile
; - {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 aFile
object.
fileFromPath(path[, filename, options]) -> {Promise<File>}
Available from formdata-node/file-from-path
subpath.
Creates a File
referencing the one on a disk by given path.
- {string} path - Path to a file
-
{string} [filename] - Optional name of the file. Will be passed as the second argument in
File
constructor. If not presented, the name will be taken from the file's path. -
{object} [options = {}] - Additional
File
options, except forlastModified
. -
{string} [options.type = ""] - Returns the media type (
MIME
) of the file represented by aFile
object.
fileFromPathSync(path[, filename, options]) -> {File}
Available from formdata-node/file-from-path
subpath.
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] - Optional name of the file. Will be passed as the second argument in
File
constructor. If not presented, the name will be taken from the file's path. -
{object} [options = {}] - Additional
File
options, except forlastModified
. -
{string} [options.type = ""] - Returns the media type (
MIME
) of the file represented by aFile
object.
isFile(value) -> {boolean}
Available from formdata-node/file-from-path
subpath.
Checks 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 -
FormDataValue
documentation on MDN. -
formdata-polyfill
HTML5FormData
for Browsers & NodeJS. -
node-fetch
a light-weight module that brings the Fetch API to Node.js -
fetch-blob
a Blob implementation on node.js, originally fromnode-fetch
. -
form-data-encoder
spec-compliantmultipart/form-data
encoder implementation. -
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.