extract-files

What is extract-files?

The extract-files package is designed to extract files from a JavaScript object tree so they can be uploaded via a multipart request. It is commonly used in applications that need to handle file uploads, especially in the context of GraphQL operations.

What are extract-files's main functionalities?

Extract files from an object

This feature allows you to extract files from an object, which is useful when preparing files for upload. The `extractFiles` function takes an object and a path to traverse within the object to find files. It returns an object with the extracted files and a clone of the original object with files replaced by null.

{"operation": "const { extractFiles } = require('extract-files');\nconst file = new File(['content'], 'file.txt', { type: 'text/plain' });\nconst operation = { variables: { file } };\nconst { files, clone } = extractFiles(operation, 'variables');"}

Support for FileList and Map objects

The package can handle `FileList` objects, which are typically obtained from file input elements, and `Map` objects. It can extract files from these complex structures, making it versatile for various file upload scenarios.

{"operation": "const { extractFiles } = require('extract-files');\nconst fileList = document.querySelector('input[type=file]').files;\nconst operation = { variables: { files: fileList } };\nconst { files, clone } = extractFiles(operation, 'variables');"}

Other packages similar to extract-files

form-data

The form-data package allows you to create `multipart/form-data` streams to submit files and values via HTTP. It can be used to simulate a form submission with file uploads, similar to extract-files, but it is more focused on constructing the form data itself rather than extracting files from an existing object structure.

busboy

Busboy is a Node.js module for parsing incoming HTML form data, including file uploads. It differs from extract-files in that it is used on the server side to process file uploads, whereas extract-files is typically used on the client side to prepare files for upload.

multer

Multer is a Node.js middleware for handling `multipart/form-data`, primarily used for uploading files. It is similar to busboy but is designed to be used with Express applications. Unlike extract-files, multer is not about extracting files from an object but rather about handling file uploads on the server side.

README

extract-files

Clones a value, recursively extracting File, Blob and ReactNativeFile instances with their object paths, replacing them with null. FileList instances are treated as File instance arrays.

Used by GraphQL multipart request spec client implementations such as graphql-react and apollo-upload-client.

Setup

To install with npm, run:

npm install extract-files

See the documentation for the function extractFiles to get started.

Support

• Node.js: ^12.20 || >= 14.13
• Browsers: > 0.5%, not OperaMini all, not IE > 0, not dead
• React Native

API

• class ReactNativeFile
• function extractFiles
• function isExtractableFile
• type ExtractableFile
• type ExtractableFileMatcher
• type ExtractFilesResult
• type ObjectPath
• type ReactNativeFileSubstitute

class ReactNativeFile

Used to mark a React Native File substitute in an object tree for extractFiles. It’s too risky to assume all objects with uri, type and name properties are files to extract.

Parameter	Type	Description
file	ReactNativeFileSubstitute	A React Native File substitute.

Examples

Ways to import.

import { ReactNativeFile } from 'extract-files';

import ReactNativeFile from 'extract-files/public/ReactNativeFile.js';

Ways to require.

const { ReactNativeFile } = require('extract-files');

const ReactNativeFile = require('extract-files/public/ReactNativeFile.js');

An extractable file in React Native.

const file = new ReactNativeFile({
  uri: uriFromCameraRoll,
  name: 'a.jpg',
  type: 'image/jpeg',
});

---

function extractFiles

Clones a value, recursively extracting File, Blob and ReactNativeFile instances with their object paths, replacing them with null. FileList instances are treated as File instance arrays.

Parameter	Type	Description
value	*	Value (typically an object tree) to extract files from.
path	ObjectPath? = ''	Prefix for object paths for extracted files.
isExtractableFile	ExtractableFileMatcher? = isExtractableFile	The function used to identify extractable files.

Returns: ExtractFilesResult — Result.

Examples

Ways to import.

import { extractFiles } from 'extract-files';

import extractFiles from 'extract-files/public/extractFiles.js';

Ways to require.

const { extractFiles } = require('extract-files');

const extractFiles = require('extract-files/public/extractFiles.js');

Extract files from an object.

For the following:

const file1 = new File(['1'], '1.txt', { type: 'text/plain' });
const file2 = new File(['2'], '2.txt', { type: 'text/plain' });
const value = {
  a: file1,
  b: [file1, file2],
};

const { clone, files } = extractFiles(value, 'prefix');

value remains the same.

clone is:

{
  "a": null,
  "b": [null, null]
}

files is a Map instance containing:

Key	Value
file1	['prefix.a', 'prefix.b.0']
file2	['prefix.b.1']

---

function isExtractableFile

Checks if a value is an extractable file.

Type: ExtractableFileMatcher

Parameter	Type	Description
value	*	Value to check.

Returns: boolean — Is the value an extractable file.

Examples

Ways to import.

import { isExtractableFile } from 'extract-files';

import isExtractableFile from 'extract-files/public/isExtractableFile.js';

Ways to require.

const { isExtractableFile } = require('extract-files');

const isExtractableFile = require('extract-files/public/isExtractableFile.js');

---

type ExtractableFile

An extractable file.

Type: File | Blob | ReactNativeFile

---

type ExtractableFileMatcher

A function that checks if a value is an extractable file.

Type: Function

Parameter	Type	Description
value	*	Value to check.

Returns: boolean — Is the value an extractable file.

See

• isExtractableFile is the default extractable file matcher.

Examples

How to check for the default exactable files, as well as a custom type of file.

import isExtractableFile from 'extract-files/public/isExtractableFile.js';

const isExtractableFileEnhanced = (value) =>
  isExtractableFile(value) ||
  (typeof CustomFile !== 'undefined' && value instanceof CustomFile);

---

type ExtractFilesResult

What extractFiles returns.

Type: object

Property	Type	Description
clone	*	Clone of the original input value with files recursively replaced with null.
files	Map<ExtractableFile, Array<ObjectPath>>	Extracted files and their locations within the original value.

---

type ObjectPath

String notation for the path to a node in an object tree.

Type: string

See

• object-path on npm.

Examples

Object path is property a, array index 0, object property b.

a.0.b

---

type ReactNativeFileSubstitute

A React Native File substitute for when using FormData.

Type: object

Property	Type	Description
uri	string	Filesystem path.
name	string?	File name.
type	string?	File content type.

See

• React Native FormData polyfill source.

Examples

A camera roll file.

const fileSubstitute = {
  uri: uriFromCameraRoll,
  name: 'a.jpg',
  type: 'image/jpeg',
};

Changelog

11.0.0

Major

• The function extractFiles now deeply clones an input value containing multiple references of an object or array with a mirrored reference structure instead of creating multiple objects or arrays. This change shouldn’t affect typical JSON.stringify use with cloned values.
• The function extractFiles now uses for…of to iterate FileList instances.

Patch

• Updated dev dependencies.
• Reverted the more specific package main field path.
• The function extractFiles now correctly handles circular references within the input value by recreating the circular references in the returned clone instead of infinitely recursing to the point of a Maximum call stack size exceeded error, fixing #14.
• Renamed imports in the test index module.
• Refactored extractFiles tests to use Object.freeze with input objects and arrays to ensure input isn’t mutated.
• Updated a code example to use a deep import.
• Amended the changelog entries for v8.0.0 and v9.0.0.