This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The DataTransfer.mozSetDataAt() method is used to add data to a specific index in the drag event's data transfer object.

A data transfer may store multiple items, each at a given zero-based index. mozSetDataAt() may only be called with an index argument less than mozItemCount in which case an existing item is modified, or equal to mozItemCount in which case a new item is added, and the mozItemCount is incremented by one.

Data should be added in order of preference, with the most specific format added first and the least specific format added last. If data of the given format already exists, it is replaced in the same position as the old data.

The data should be either a string, a Boolean or number type (which will be converted into a string) or an nsISupports.

Note: This method is Gecko-specific.


void dataTransfer.mozSetDataAt([type], data, index);


A string representing the type of the drag data to add to the drag data object.
A nsIVariant representing the data to add to the drag data object.
A unsigned long representing the index of the data to add.

Return value



This example shows the use of the mozSetDataAt() method in a dragstart handler.

function dragstart_handler(event)
  var dt = event.dataTransfer;
  var idx = dt.mozItemCount;
  // Add two new items to the drag transfer 
  if (idx >= 0) {
    dt.mozSetDataAt("text/uri-list","", idx);
    dt.mozSetDataAt("text/html", "Hello World", idx+1);


This method is not defined in any Web standard.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
No support No support (Yes) No support No support No support
Feature Android Android Webview Chrome for Android Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile
Basic support No support No support No support ? ? No support No support No support

[1]Partial support refers to not supporting .setDragImage []

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API drag and drop Method Non-standard Reference