Drag and drop custom clipboard contents from OS

[Martin Ceronio]

This list of clipboard formats refers:

https://msdn.microsoft.com/en-us/library/windows/desktop/ff729168(v=vs.85).aspx

It seems that only a limited set of clipboard formats is supported for dragging from the OS into an HTML5 drop target.

To test this, I have created an HTML5 drop target on a page and played around by dragging data from various applications into it and examining the contents of event.dataTransfer in debugging. In most cases, there will be something available in dataTransfer.item and via dataTransfer.getData(), but there are some exceptions, especially when the source seems to use some custom clipboard format. (Tested on Windows with Chrome, Firefox and IE).

Is this specifically something in the HTML5 specification? I tried looking through the W3 spec on drag & drop (which is pretty big), but my guess is that at the point the browser creates the drag event, it is filtering out the clipboard contents on format.

I would really like to know, otherwise, how one would be able to access custom clipboard contents, or raw clipboard data in the drop.

(Sorry if this is the wrong place to post this, but hopefully you can steer me in the right direction or explain, in terms of implementation, what the reasoning behind this behaviour is).

[Martin Ceronio]

I think I have found the answer (which I have posted on SO here: https://stackoverflow.com/a/47385597/274354).

It seems to me that the list of clipboard formats for drag and drop is indeed limited and does not support custom clipboard formats.

[Daniel Cheng]

Unfortunately, for privacy and security reasons, Chrome limits the native clipboard types that get exposed to the web API. The web API *does* support arbitrary format strings, and any custom formats will be visible to other web pages--just not native apps.

https://github.com/w3c/clipboard-apis/issues/46 has some more background.

Daniel

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