# FormData

FormData implementation for Node.js. Built over Readable stream and async generators.
Can be used to communicate between servers with multipart/form-data format.

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## Installation

You can install this package from npm:

```
npm install formdata-node
```

Or with yarn:

```
yarn add formdata-node
```

## Usage

FormData instance have `.pipe()` and `.[Symbol.asyncIterator]()` methods
to get an access to the internal Readable stream. You can also get the stream
from `FormData#stream` getter.

You can send queries via HTTP clients that supports headers setting Readable stream as body.

Let's take a look at minimal example with [got](https://github.com/sindresorhus/got):

```js
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: {
    // Assign required headers to the request manually.
    // We need to set a content type and boundary.
    "content-type": `multipart/form-data; boundary=${fd.boundary}`
    // Or you can use FormData#headers to get an object with content-type
    // header, like this: ...fd.headers
    // this will be equivalent of code from above
  }
}

got.post("http://example.com", options)
  .then(res => console.log("Res: ", res.body))
  .catch(err => console.error("Error: ", err))
```

## API

### `constructor FormData([fields])`

Initialize new FormData instance

  - **{array}** [fields = null] – an optional FormData initial fields.
    Each initial field should be passed as an array with 3 elemtnts
    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

##### `get boundary() -> {string}`

Returns a boundary string of the current FormData instance.

##### `get stream() -> {stream.Readable}`

Returns an internal Readable stream.

##### `get headers() -> {object}`

Returns object with `content-type` header

#### 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**
  - **{any}** value – The field value. You can pass any JavaScript primitive type (including **null** and **undefined**),
    **[Buffer](https://nodejs.org/api/buffer.html#buffer_buffer)** or **[Readable](https://nodejs.org/api/stream.html#stream_class_stream_readable)** stream.
    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** and **Readable** .

##### `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.

  - **{string}** name – The name of the field whose data is contained in **value**
  - **{any}** value – The field value. You can pass any JavaScript primitive type (including **null** and **undefined**),
    **[Buffer](https://nodejs.org/api/buffer.html#buffer_buffer)** or **[Readable](https://nodejs.org/api/stream.html#stream_class_stream_readable)** stream.
    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** and **Readable** .

##### `get(name) -> {string | Buffer | stream.Readable}`

Returns the first value associated with the given name.
**Buffer** and **Readable** values will be returned as-is.

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

##### `getAll(name) -> {Array<string | Buffer | stream.Readable>}`

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}`

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.

#### `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:
    + **{any}** 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
  - **{any}** [ctx = null] – Value to use as **this** context when executing the given **callback**

##### `keys() -> {iterator}`

Returns an **[iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols)** allowing to go through the **FormData** keys

##### `values() -> {iterator}`

Returns an **[iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols)** allowing to go through the **FormData** values

##### `entries() -> {iterator}`

Returns an **[iterator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols)** allowing to go through the **FormData** key/value pairs

##### `[Symbol.iterator]() -> {iterator}`

An alias of [FormData#entries](#entries---iterator)

##### `[Symbol.asyncIterator]() -> {asyncIterator}`

Returns an async iterator allowing to read a data from internal Readable stream using **for-await** syntax.
Read the [async iteration proposal](https://github.com/tc39/proposal-async-iteration) to get more info about async iterators.

## Related links

  - [then-busboy](https://github.com/octet-stream/then-busboy) is 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](https://github.com/octet-stream/object-to-form-data) converts JavaScript object to FormData.
  - [FormData](https://developer.mozilla.org/en-US/docs/Web/API/FormData) interface documentation on MDN