MultipleUpload JavaScript upload component
Works with any backend npm install Zero dependencies
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Pick files straight from Box.com (enterprise content cloud)

Built-in Box adapter. OAuth 2.0 implicit flow in a popup; lists the user's root folder and surfaces a clean picker UI. Returns RemoteFile[] with bearer-token-authorized download URLs that your server's /import-url endpoint can fetch with NDJSON live progress. Completes the enterprise cloud-picker quartet: Google Drive + Dropbox + OneDrive + Box.

Setup required. Create a Box app at app.box.com/developers/console (Custom App -> User Authentication (OAuth 2.0)). Set the redirect URI to your origin, then configure: 
MultipleUpload.configureRemoteSource('box', {
 clientId: 'YOUR_BOX_CLIENT_ID',
 redirectUri: window.location.origin // optional; auto-derived if omitted
});
Returned RemoteFile shape
{
 url: 'https://api.box.com/2.0/files/123456789/content',
 fileName: 'enterprise-report.pdf',
 fileSize: 2_457_600,
 headers: { 'Authorization': 'Bearer abc123...' } // attached when fetching
}
Auth flow
  1. User clicks the Box button rendered by remoteSources: ['box'].
  2. Adapter opens a popup -> Box's OAuth 2.0 implicit-grant screen.
  3. On approve, Box redirects to your redirectUri with #access_token=... in the URL fragment.
  4. Adapter detects the redirect (polling popup.location.href until same-origin), extracts the token, closes the popup.
  5. Fetches the user's root folder listing via the Box REST API.
  6. Renders a minimal picker modal with checkbox / radio selection.
  7. Picked files resolve as RemoteFile[] with Authorization headers attached.
  8. Each file flows into uploader.importFromUrl(url, { headers }) -> your server fetches the bytes from Box using the bearer.
Cloud picker quartet
SourceAuthPicker UISetup
'googledrive'OAuth (gsi)Google Picker (full-featured){ apiKey, clientId }
'dropbox'OAuth (popup)Dropbox dropins.js{ appKey }
'onedrive'OAuth (popup)OneDrive.js v7.2{ clientId }
'box'OAuth (popup)Built-in minimal picker (root folder){ clientId }
Mix and match
// One uploader, all four cloud sources side by side
new MultipleUpload('#uploader', {
 remoteSources: ['googledrive', 'dropbox', 'onedrive', 'box']
});

// Plus your own custom adapter
MultipleUpload.registerRemoteSource('internal-cms', {
 title: 'Company CMS',
 icon: '<svg .../>',
 pick: async (uploader) => {
 const picked = await openMyCmsPicker();
 return picked.map(p => ({ url: p.cdnUrl, fileName: p.name }));
 }
});
Why a built-in picker UI for Box

Box doesn't ship an official browser-side file-picker SDK like Dropbox / OneDrive / Drive - historically integrators have had to roll their own. The built-in adapter ships a minimal modal that lists the user's root folder with checkbox selection. For deeper navigation (subfolders, search), override the adapter:

MultipleUpload.registerRemoteSource('box', {
 title: 'Box (custom)',
 icon: '<svg .../>',
 ready: () => !!myCustomBoxConfig.clientId,
 pick: myCustomBoxFlow // your richer picker
});