Saturday, February 9, 2013

Drag and Drop In HTML 5

Drag and Drop

Drag and drop is a very common feature. It is when you "grab" an object and drag it to a different location.
In HTML5, drag and drop is part of the standard, and any element can be draggable.

Browser Support

Internet ExplorerFirefoxOperaGoogle ChromeSafari
Internet Explorer 9, Firefox, Opera 12, Chrome, and Safari 5 support drag and drop.
Note: Drag and drop does not work in Safari 5.1.2.

HTML5 Drag and Drop Example

The example below is a simple drag and drop example:


function allowDrop(ev)

function drag(ev)

function drop(ev)
var data=ev.dataTransfer.getData("Text");;

<div id="div1" ondrop="drop(event)"

<img id="drag1" src="img_logo.gif" draggable="true"
ondragstart="drag(event)" width="336" height="69">


It might seem complicated, but lets go through all the different parts of a drag and drop event.

Make an Element Draggable

First of all: To make an element draggable, set the draggable attribute to true:
<img draggable="true">

What to Drag - ondragstart and setData()

Then, specify what should happen when the element is dragged.
In the example above, the ondragstart attribute calls a function, drag(event), that specifies what data to be dragged.
The dataTransfer.setData() method sets the data type and the value of the dragged data:
function drag(ev)
In this case, the data type is "Text" and the value is the id of the draggable element ("drag1").

Where to Drop - ondragover

The ondragover event specifies where the dragged data can be dropped.
By default, data/elements cannot be dropped in other elements. To allow a drop, we must prevent the default handling of the element.
This is done by calling the event.preventDefault() method for the ondragover event:

Do the Drop - ondrop

When the dragged data is dropped, a drop event occurs.
In the example above, the ondrop attribute calls a function, drop(event):
function drop(ev)
var data=ev.dataTransfer.getData("Text");;
Code explained:
  • Call preventDefault() to prevent the browser default handling of the data (default is open as link on drop)
  • Get the dragged data with the dataTransfer.getData("Text") method. This method will return any data that was set to the same type in the setData() method
  • The dragged data is the id of the dragged element ("drag1")
  • Append the dragged element into the drop element
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