Questions about implementing `clipboard.write`

[trflynn89]

In the following steps, iterating over itemList:

https://w3c.github.io/clipboard-apis/#dom-clipboard-write

4. For each clipboardItem in dataList:
    1. For each representation in clipboardItem’s clipboard item's list of representations:
        (in this loop, we add items to `itemList`
    2. For each blob in itemList:
        5. Append cleanItem to cleanItemList.
    3. Let option be clipboardItem’s clipboard item's presentation style.
    4. Write blobs and option to the clipboard with cleanItemList and option.

After we writecleanItemList to the clipboard, we do not clear itemList over clearItemList. So on the next iteration of dataList, won't we write those same items again? These lists will just keep growing as we loop over dataList.

---

In the same steps, the spec seems to assume that the "2. React to representationDataPromise:" step will react synchronously. In practice, this occurs asynchronously, because even when the promise is already resolved, the reaction steps ultimately queue a microtask to run the fulfillment/rejection steps (via HostEnqueuePromiseJob).

[EdgarChen]

In the following steps, iterating over itemList:

https://w3c.github.io/clipboard-apis/#dom-clipboard-write

4. For each clipboardItem in dataList:
    1. For each representation in clipboardItem’s clipboard item's list of representations:
        (in this loop, we add items to `itemList`
    2. For each blob in itemList:
        5. Append cleanItem to cleanItemList.
    3. Let option be clipboardItem’s clipboard item's presentation style.
    4. Write blobs and option to the clipboard with cleanItemList and option.

After we writecleanItemList to the clipboard, we do not clear itemList over clearItemList. So on the next iteration of dataList, won't we write those same items again? These lists will just keep growing as we loop over dataList.

Perhaps the declaration of itemList and cleanItemList should be moved into the iteration of dataList?

In the same steps, the spec seems to assume that the "2. React to representationDataPromise:" step will react synchronously. In practice, this occurs asynchronously, because even when the promise is already resolved, the reaction steps ultimately queue a microtask to run the fulfillment/rejection steps (via HostEnqueuePromiseJob).

Yes, and the write-to-clipboard step should wait until all promises are resolved.

[trflynn89]

Perhaps the declaration of itemList and cleanItemList should be moved into the iteration of dataList?

Yep that works, and is actually how we ended up implementing this method in Ladybird:

https://github.com/LadybirdBrowser/ladybird/blob/912009f6b37f76891474f58e2df55b2d946b6788/Libraries/LibWeb/Clipboard/Clipboard.cpp#L441-L443

[johanneswilm]

TPAC 2025:

Smaug
There seem to be a proposal
Rohan
The proposal in the issue looks good. Can we come to a resolution
Smaug
The proposal looks fine. Needs PR
Johannes
Are there any opposition to the proposal
There is an agreement.