The DataTransferItem object represents one drag data item. During a drag operation, each drag event has a dataTransfer property which contains a list of drag data items. Each item in the list is a DataTransferItem object.
The read-only DataTransferItem.type property returns the type (format) of the DataTransferItem object representing the drag data item. The type is a Unicode string generally given by a MIME type, although a MIME type is not required.