The DataTransfer object is used to hold the data that is being dragged during a drag and drop operation. It may hold one or more data items, each of one or more data types. For more information about drag and drop, see HTML Drag and Drop API.
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.
If the item is a file, the DataTransferItem.getAsFile() method returns the drag data item's File object. If the item is not a file, this method returns null.
The DataTransferItem.getAsString() method invokes the given callback with the drag data item's string data as the argument if the item's kind is a Plain unicode string (i.e. kind is string).
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.
The DataTransferItemList object is a list of DataTransferItem objects representing items being dragged. During a drag operation, each DragEvent has a dataTransfer property and that property is a DataTransferItemList.
The DataTransferItemList.add() method creates a new DataTransferItem using the specified data and adds it to the drag data list. The item may be a File or a string of a given type. If the item is successfully added to the list, the newly-created DataTransferItem object is returned.
The DataTransferItemList() getter method implements support for accessing items in the DataTransferItemList using array-style syntax (that is DataTransferItemList[index]).
The read-only DataTransferItemList.length property returns the number of items in the list. If the list has no items, or is disabled (because it has no data store at all), this property returns zero.
The DataTransferItemList.remove() method removes the DataTransferItem at the specified index from the list. If the index is less than zero or greater than one less than the length of the list, the list will not be changed.