Websites are currently able to provide functionality for uploading files by using
<input type="file" multiple> and drag and drop. However, there currently is no standard and interoperable spec that enables the handling of directories and cases that involve a mix of files and directories.
We are proposing a spec that will provide the necessary mechanisms to enable directory uploading which can be found here: https://wicg.github.io/directory-upload/proposal.html
This has been worked on by Microsoft - with contributions from Mozilla - and we would like to get feedback from the wider WICG before we are able to migrate it to a working group in the W3C. A polyfill that uses the old Chrome FileSystem API - which has since been deprecated - can be found here: https://wicg.github.io/directory-upload/index.html
Your feedback to our proposal is greatly appreciated!