eventdataTransferdropEffect

Event.dataTransfer.dropEffect is a property in the HTML5 Drag and Drop API that signals the operation intended to be performed on the dragged data if a drop occurs. The dropEffect value is read and/or set during drag events, most commonly in dragover or dragenter, and is considered when determining the final drop action during the drop event. The value is a string that represents the requested operation.

Possible values for dropEffect are "none", "copy", "move", and "link". "none" indicates that no drop is allowed. "copy" suggests that the data should be duplicated at the drop target. "move" indicates that the data should be transferred from the source to the destination. "link" implies that a link to the data should be created at the drop site. The exact effect that occurs depends on the intersection of the dropTarget's requested dropEffect and the source’s allowed operations.

Usage typically involves handling a dragover event, calling preventDefault to indicate a drop is possible, and setting event.dataTransfer.dropEffect to the desired value. In the drop event, the implementation should perform the corresponding operation (copy, move, or link) while ensuring the chosen effect is compatible with the source’s effectAllowed setting.

Compatibility is broad across modern browsers, though subtle differences exist in how visual cues and restrictions are enforced. The concept remains a key part of controlling user interaction during drag-and-drop workflows. See also: DataTransfer, Drag and Drop API, effectAllowed.