Intent to Ship: Preserving dropEffect Values from dragover to drop Events

[Chromestatus]

Contact emails

ror...@microsoft.com

Specification

https://www.w3.org/TR/2011/WD-html5-20110113/dnd.html#dom-datatransfer-dropeffect

Summary

The HTML5 Drag and Drop API allows web applications to handle drag-and-drop operations through a series of events: `dragstart`, `dragenter`, `dragover`, `dragleave`, `drop`, and `dragend`. During these events, the [`dataTransfer.dropEffect`](https://www.w3.org/TR/2011/WD-html5-20110113/dnd.html#dom-datatransfer-dropeffect) property indicates which operation (copy, move, link, or none) should be performed. According to the [HTML5 specification](https://www.w3.org/TR/2011/WD-html5-20110113/dnd.html#dndevents), the `dropEffect` value set by web applications during the last `dragover` event should be preserved and available in the subsequent `drop` event. However, Chromium-based browsers were overwriting the web application's `dropEffect` value with the browser's own negotiated operation before the `drop` event fired, breaking specification compliance and limiting developer control over drag-and-drop behavior.

Blink component

Blink>DataTransfer

Web Feature ID

draganddrop

Motivation

The current behavior: - Violates the HTML5 specification: Contradicts the standardized behavior defined in the HTML5 Drag and Drop API - Breaks developer control: Removes the ability for web applications to manage their own drag-and-drop operations - Creates unpredictable UX: The operation indicated during drag (via cursor feedback) may not match what's available in the drop handler - Forces workarounds: Developers must store `dropEffect` values in global variables or custom data attributes rather than using the standard API - Limits functionality: Makes it impossible to build spec-compliant file managers, code editors, and other applications requiring sophisticated drag-and-drop

Initial public proposal

No information provided

Search tags

draganddrop, dropEffect

TAG review

No information provided

TAG review status

Not applicable

Risks

Interoperability and Compatibility

No information provided

Gecko: Shipped/Shipping

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/596)

Web developers: Strongly positive (https://issues.chromium.org/issues/40068941) 42 upvotes on the associated Chromium issue

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

None

Debuggability

No new functionality needed for debuggability

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes
This is a blink level change independent of platform implementation.

Is this feature fully tested by web-platform-tests?

Yes
There are few manual WPTs like https://wpt.live/html/editing/dnd/drop/025.html which cover this feature. Chromium has internal web tests / unit tests as well for this feature.

Flag name on about://flags

No information provided

Finch feature name

PreserveDropEffect

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/40068941

Estimated milestones

Shipping on desktop	146
Shipping on Android	146
Shipping on WebView	146

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

No information provided

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5140028068069376?gate=6545001561587712

This intent message was generated by Chrome Platform Status.

[Alex Russell]

LGTM1

[Philip Jägenstedt]

Hi Rohan,

I tried https://wpt.live/html/editing/dnd/drop/025.html in Firefox (macOS) and it fails, but in a different way from Chrome. Does this test match the spec, and if it does will Chrome fully pass it with these changes? I'm trying to understand if we are going to match Firefox in the details here.

Also, can this test be automated, and if not what kind of testing infrastructure is missing?

Best regards,

Philip

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[Rohan Raja]

Thanks Alex and Philip for reviewing this intent.

Without the dropEffect fix, the https://wpt.live/html/editing/dnd/drop/025.html WPT prints:
"FAIL: drag dropEffect move instead of none
dragenter dropEffect none instead of copy
dragover dropEffect none instead of copy
dragover dropEffect none instead of copy on second attempt
drop dropEffect none instead of link
dragend dropEffect link instead of move"

After applying the fix (setting --enable-blink-features=PreserveDropEffect flag in Chromium), the WPT still has two failures independent of this feature:
"FAIL: drag dropEffect move instead of none
dragend dropEffect link instead of move"

Both these failures seem to be existing bugs in Chromium (and even in Firefox) since they don't match the spec. I have logged spec mis-match bugs for the same in Chromium. The details can be found in the bug descriptions below:
- https://issues.chromium.org/issues/475998132
- https://issues.chromium.org/issues/475998138

Regarding automation of this WPT, the testharness in wpt infra seem to already provide helper functions to simulate drag/drop behaviour (like done here https://chromium-review.googlesource.com/c/chromium/src/+/6955024). There is an ongoing effort for automating the manual DnD tests which is being tracked here - https://issues.chromium.org/issues/40216874. The last change appears to be from a few months ago, so I will follow up with the owner to see if any help is needed. Meanwhile, in Chromium we do have internal automated web tests which cover this feature - https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/fast/events/drag-and-drop/drop-effect-preservation-basic.html?q=third_party%2Fblink%2Fweb_tests%2Ffast%2Fevents%2Fdrag-and-drop%2Fdrop-effect-preservation-basic.html

Thanks

Rohan Raja

[Rick Byers]

This seems like a bugfix to me and the web compat risk seems likely to be low so presence of a killswitch flag seems adequate to me. LGTM2

Thank you for working to improve DnD spec conformance and utility, I know it needs it!

To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/3e1a82d8-37cb-4cb4-a148-2015c5db14a7n%40chromium.org.

[Philip Jägenstedt]

LGTM3

Thanks Rohan for digging into the testing situation. It's great to hear that there's already an effort to automate DnD tests, and it would be great if this test can be moved over to the new infrastructure. If that's already possible with the work that has already landed, it would be great if you can give it a try as part of shipping this change.

[Rohan Raja]

Thanks Rick and Philip. 

And yes - I will try and automate the existing manual test for this feature as part of shipping it.

[Masataka Yakura]

On Tuesday, January 13, 2026 at 2:37:15 PM UTC+9 Chromestatus wrote:

Contact emails

ror...@microsoft.com

Specification

https://www.w3.org/TR/2011/WD-html5-20110113/dnd.html#dom-datatransfer-dropeffect 

Summary

The HTML5 Drag and Drop API allows web applications to handle drag-and-drop operations through a series of events: `dragstart`, `dragenter`, `dragover`, `dragleave`, `drop`, and `dragend`. During these events, the [`dataTransfer.dropEffect`](https://www.w3.org/TR/2011/WD-html5-20110113/dnd.html#dom-datatransfer-dropeffect) property indicates which operation (copy, move, link, or none) should be performed. According to the [HTML5 specification](https://www.w3.org/TR/2011/WD-html5-20110113/dnd.html#dndevents), the `dropEffect` value set by web applications during the last `dragover` event should be preserved and available in the subsequent `drop` event. However, Chromium-based browsers were overwriting the web application's `dropEffect` value with the browser's own negotiated operation before the `drop` event fired, breaking specification compliance and limiting developer control over drag-and-drop behavior.

That spec link is quite outdated; it points to the 2011 snapshot. I'm curious if the spec has been updated since then.

https://html.spec.whatwg.org/multipage/dnd.html#dom-datatransfer-dropeffect