This is the core module that orchestrates everything in Uppy, managing state and events and providing methods.

const Uppy = require('@uppy/core')

const uppy = Uppy()


Install from NPM:

npm install @uppy/core

In the CDN package, it is available on the Uppy global object:

const Core = Uppy.Core


The Uppy core module has the following configurable options:

const uppy = Uppy({
  id: 'uppy',
  autoProceed: false,
  allowMultipleUploads: true,
  debug: false,
  restrictions: {
    maxFileSize: null,
    maxNumberOfFiles: null,
    minNumberOfFiles: null,
    allowedFileTypes: null
  meta: {},
  onBeforeFileAdded: (currentFile, files) => currentFile,
  onBeforeUpload: (files) => {},
  locale: defaultLocale,
  store: new DefaultStore()

id: 'uppy'

A site-wide unique ID for the instance.

If multiple Uppy instances are being used, for instance, on two different pages, an id should be specified. This allows Uppy to store information in localStorage without colliding with other Uppy instances.

Note that this ID should be persistent across page reloads and navigation—it shouldn’t be a random number that is different every time Uppy is loaded.
For example, if one Uppy instance is used to upload user avatars, and another to add photos to a blog post, you might use:

const avatarUploader = Uppy({ id: 'avatar' })
const photoUploader = Uppy({ id: 'post' })

autoProceed: false

By default Uppy will wait for an upload button to be pressed in the UI, or an .upload() method to be called, before starting an upload. Setting this to autoProceed: true will start uploading automatically after the first file is selected.

allowMultipleUploads: true

Whether to allow multiple upload batches. This means multiple calls to .upload(), or a user adding more files after already uploading some. An upload batch is made up of the files that were added since the previous .upload() call.

With this option set to true, users can upload some files, and then add more files and upload those as well. A model use case for this is uploading images to a gallery or adding attachments to an email.

With this option set to false, users can upload some files, and you can listen for the ‘complete’ event to continue to the next step in your app’s upload flow. A typical use case for this is uploading a new profile picture. If you are integrating with an existing HTML form, this option gives the closest behaviour to a bare <input type="file">.

restrictions: {}

Optionally, provide rules and conditions to limit the type and/or number of files that can be selected.


  • maxFileSize null | number — maximum file size in bytes for each individual file (total max size has been requested, and is planned)
  • maxNumberOfFiles null | number — total number of files that can be selected
  • minNumberOfFiles null | number — minimum number of files that must be selected before the upload
  • allowedFileTypes null | array of wildcards image/*, exact mime types image/jpeg, or file extensions .jpg: ['image/*', '.jpg', '.jpeg', '.png', '.gif']

maxNumberOfFiles also affects the number of files a user is able to select via the system file dialog in UI plugins like DragDrop, FileInput and Dashboard: when set to 1, they will only be able to select a single file. When null or another number is provided, they will be able to select multiple files.

allowedFileTypes gets passed to the system file dialog via <input>’s accept attribute, so only files matching these types will be selectable.

meta: {}

Metadata object, used for passing things like public keys, usernames, tags and so on:

meta: {
  username: 'John'

This global metadata is added to each file in Uppy. It can be modified by two methods:

  1. uppy.setMeta({ username: 'Peter' }) — set or update meta for all files.
  2. uppy.setFileMeta('myfileID', { resize: 1500 }) — set or update meta for specific file.

Metadata from each file is then attached to uploads in Tus and XHRUpload plugins.

Metadata can also be added from a <form> element on your page, through the Form plugin or through the UI if you are using Dashboard with the metaFields option.

onBeforeFileAdded: (currentFile, files) => currentFile

A function run before a file is added to Uppy. It gets passed (currentFile, files) where currentFile is a file that is about to be added, and files is an object with all files that already are in Uppy.

Use this function to run any number of custom checks on the selected file, or manipulate it, for instance, by optimizing a file name.

Return true/nothing or a modified file object to proceed with adding the file:

onBeforeFileAdded: (currentFile, files) => {
  if (currentFile.name === 'forest-IMG_0616.jpg') {
    return true

// or

onBeforeFileAdded: (currentFile, files) => {
  const modifiedFile = Object.assign(
    { name: currentFile + Date.now()
  return modifiedFile

Return false to abort adding the file:

onBeforeFileAdded: (currentFile, files) => {
  if (!currentFile.type) {
    // log to console
    uppy.log(`Skipping file because it has no type`)
    // show error message to the user
    uppy.info(`Skipping file because it has no type`, 'error', 500)
    return false

Note: it is up to you to show a notification to the user about a file not passing validation. We recommend showing a message using uppy.info() and logging to console for debugging purposes.

onBeforeUpload: (files) => files

A function run before an upload begins. Gets passed files object with all the files that are already in Uppy.

Use this to check if all files or their total number match your requirements, or manipulate all the files at once before upload.

Return true or modified files object to proceed:

onBeforeUpload: (files) => {
  const updatedFiles = Object.assign({}, files)
  Object.keys(updatedFiles).forEach(fileId => {
    updatedFiles[fileId].name = 'myCustomPrefix_' + updatedFiles[fileId].name
  return updatedFiles

Return false to abort:

onBeforeUpload: (files) => {
  if (Object.keys(files).length < 2) {
    // log to console
    uppy.log(`Aborting upload because only ${Object.keys(files).length} files were selected`)
    // show error message to the user
    uppy.info(`You have to select at least 2 files`, 'error', 500)
    return false

Note: it is up to you to show a notification to the user about a file not passing validation. We recommend showing a message using uppy.info() and logging to console for debugging purposes.

locale: {}

This allows you to override language strings:

locale: {
  strings: {
    youCanOnlyUploadX: {
      0: 'You can only upload %{smart_count} file',
      1: 'You can only upload %{smart_count} files'
    youHaveToAtLeastSelectX: {
      0: 'You have to select at least %{smart_count} file',
      1: 'You have to select at least %{smart_count} files'
    exceedsSize: 'This file exceeds maximum allowed size of',
    youCanOnlyUploadFileTypes: 'You can only upload:',
    companionError: 'Connection with Companion failed'

It also offers the pluralization function, which is used to determine which string will be used for the provided smart_count number.

For example, for the Icelandic language, the pluralization function would be:

locale: {
  pluralize: (n) => (n % 10 !== 1 || n % 100 === 11) ? 1 : 0

We are using a forked Polyglot.js.

store: defaultStore()

The Store that is used to keep track of internal state. By default, a simple object is used.

This option can be used to plug Uppy state into an external state management library, such as Redux. You can then write custom views with the library that is also used by the rest of the application.


uppy.use(plugin, opts)

Add a plugin to Uppy, with an optional plugin options object.

const Uppy = require('@uppy/core')
const DragDrop = require('@uppy/drag-drop')

const uppy = Uppy()
uppy.use(DragDrop, { target: 'body' })


Uninstall and remove a plugin.


Get a plugin by its id to access its methods.


Get the Uppy instance ID, see the id option.


Add a new file to Uppy’s internal state.

  name: 'my-file.jpg', // file name
  type: 'image/jpeg', // file type
  data: blob, // file blob
  source: 'Local', // optional, determines the source of the file, for example, Instagram
  isRemote: false // optional, set to true if actual file is not in the browser, but on some remote server, for example, when using companion in combination with Instagram

addFile gives an error if the file cannot be added, either because onBeforeFileAdded(file) gave an error, or because uppy.opts.restrictions checks failed.

If uppy.opts.autoProceed === true, Uppy will begin uploading automatically when files are added.

Sometimes you might need to add a remote file to Uppy. This can be achieved by fetching the file, then creating a Blob object, or using the Url plugin with Companion.


Remove a file from Uppy.


Removing a file that is already being uploaded cancels that upload.


Get a specific file object by its ID.

const file = uppy.getFile('uppyteamkongjpg1501851828779')

file.id        // 'uppyteamkongjpg1501851828779'
file.name      // 'nature.jpg'
file.extension // '.jpg'
file.type      // 'image/jpeg'
file.data      // the Blob object
file.size      // 3947642 (returns 'N/A' if size cannot be determined)
file.preview   // value that can be used to populate "src" attribute of an "img" tag


Get an array of all file objects in Uppy. See uppy.getFile() for an example of the file object format.

const prettyBytes = require('pretty-bytes')
const items = uppy.getFiles().map(() =>
  `<li>${file.name} - ${prettyBytes(file.size)}</li>`
document.querySelector('.file-list').innerHTML = `<ul>${items}</ul>`


Start uploading selected files.

Returns a Promise result that resolves with an object containing two arrays of uploaded files:

  • result.successful - Files that were uploaded successfully.
  • result.failed - Files that did not upload successfully. These file objects will have a .error property describing what went wrong.
uppy.upload().then((result) => {
  console.info('Successful uploads:', result.successful)

  if (result.failed.length > 0) {
    result.failed.forEach((file) => {


Toggle pause/resume on an upload. Will only work if resumable upload plugin, such as Tus, is used.


Pause all uploads. Will only work if a resumable upload plugin, such as Tus, is used.


Resume all uploads. Will only work if resumable upload plugin, such as Tus, is used.


Retry an upload (after an error, for example).


Retry all uploads (after an error, for example).


Cancel all uploads, reset progress and remove all files.


Update Uppy’s internal state. Usually, this method is called internally, but in some cases it might be useful to alter something directly, especially when implementing your own plugins.

Uppy’s default state on initialization:

  plugins: {},
  files: {},
  currentUploads: {},
  capabilities: {
    resumableUploads: false
  totalProgress: 0,
  meta: Object.assign({}, this.opts.meta),
  info: {
    isHidden: true,
    type: 'info',
    message: ''

Updating state:

  smth: true

State in Uppy is considered to be immutable. When updating values, it is your responsibility to not mutate them, but instead create copies. See Redux docs for more info on this. Here is an example from Uppy.Core that updates progress for a particular file in state:

// We use Object.assign({}, obj) to create a copy of `obj`.
const updatedFiles = Object.assign({}, uppy.getState().files)
// We use Object.assign({}, obj, update) to create an altered copy of `obj`.
const updatedFile = Object.assign({}, updatedFiles[fileID], {
  progress: Object.assign({}, updatedFiles[fileID].progress, {
    bytesUploaded: data.bytesUploaded,
    bytesTotal: data.bytesTotal,
    percentage: Math.floor((data.bytesUploaded / data.bytesTotal * 100).toFixed(2))
updatedFiles[data.id] = updatedFile
uppy.setState({files: updatedFiles})


Returns the current state from the Store.

uppy.setFileState(fileID, state)

Update the state for a single file. This is mostly useful for plugins that may want to store data on file objects, or that need to pass file-specific configurations to other plugins that support it.

fileID is the string file ID. state is an object that will be merged into the file’s state object.



Alters global meta object in state, the one that can be set in Uppy options and gets merged with all newly added files. Calling setMeta will also merge newly added meta data with previously selected files.

uppy.setMeta({ resize: 1500, token: 'ab5kjfg' })

uppy.setFileMeta(fileID, data)

Update metadata for a specific file.

uppy.setFileMeta('myfileID', { resize: 1500 })


Stop all uploads in progress and clear file selection, set progress to 0. Basically, return things to the way they were before any user input.


Uninstall all plugins and close down this Uppy instance. Also runs uppy.reset() before uninstalling.



  • message {string}
  • type {string=} error or warning

Logs stuff to console, only if uppy.opts.debug is set to true. Silent in production.

uppy.log('[Dashboard] adding files...')



  • message {(string|object)}'info message' or { message: 'Oh no!', details: 'File couldn’t be uploaded' }
  • type {string} [type=’info’]info, warning, success or error
  • duration {number} [duration = 3000] — in milliseconds

Sets a message in state, with optional details, that can be shown by notification UI plugins. Currently, that means just the Informer plugin, included by default in Dashboard.

this.info('Oh my, something good happened!', 'success', 3000)
    message: 'Oh no, something bad happened!',
    details: 'File couldn’t be uploaded because there is no internet connection',
  }, 'error', 5000)

info-visible and info-hidden events are emitted when this info message should be visible or hidden.

uppy.on('event', action)

Subscribe to an uppy-event. See below for the full list of events.

uppy.off('event', action)

Unsubscribe to an uppy-event. See below for the full list of events.


Uppy exposes events that you can subscribe to in your app:


Fired each time a file is added.

uppy.on('file-added', (file) => {
  console.log('Added file', file)


Fired each time a file is removed.

uppy.on('file-removed', (file) => {
  console.log('Removed file', file)


Fired when upload starts.

uppy.on('upload', (data) => {
  // data object consists of `id` with upload ID and `fileIDs` array
  // with file IDs in current upload
  // data: { id, fileIDs }
  console.log(`Starting upload ${id} for files ${fileIDs}`)


Fired each time file upload progress is available:

uppy.on('upload-progress', (file, progress) => {
  // file: { id, name, type, ... }
  // progress: { uploader, bytesUploaded, bytesTotal }
  console.log(file.id, progress.bytesUploaded, progress.bytesTotal)


Fired each time a single upload is completed.

response object (depending on the uploader plugin used, it might contain less info, the example is for @uppy/xhr-upload):

  status, // HTTP status code (0, 200, 300)
  body, // response body
  uploadURL // the file url, if it was returned
uppy.on('upload-success', (file, response) => {
  console.log(file.name, response.uploadURL)
  var img = new Image()
  img.width = 300
  img.alt = file.id
  img.src = response.uploadURL


Fired when all uploads are complete.

The result parameter is an object with arrays of successful and failed files, just like in uppy.upload()’s return value.

uppy.on('complete', (result) => {
  console.log('successful files:', result.successful)
  console.log('failed files:', result.failed)


Fired when Uppy fails to upload/encode the entire upload. That error is then set to uppy.getState().error.


Fired each time a single upload has errored.

response object (depending on the uploader plugin used, it might contain less info, the example is for @uppy/xhr-upload):

  status, // HTTP status code (0, 200, 300)
  body // response body
uppy.on('upload-error', (file, error, response) => {
  console.log('error with file:', file.id)
  console.log('error message:', error)


Fired when an upload has been retried (after an error, for example):

uppy.on('upload-retry', (fileID) => {
  console.log('upload retried:', fileID)


Fired when “info” message should be visible in the UI. By default, Informer plugin is displaying these messages (enabled by default in Dashboard plugin). You can use this event to show messages in your custom UI:

uppy.on('info-visible', () => {
  const info = uppy.getState().info
  // info: {
  //  isHidden: false,
  //  type: 'error',
  //  message: 'Failed to upload',
  //  details: 'Error description'
  // }
  alert(`${info.message} ${info.details}`)


Fired when “info” message should be hidden in the UI. See info-visible.


Fired when uppy.cancelAll() is called, all uploads are canceled, files removed and progress is reset.