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.

HTML Drag and Drop Example

The example below is a simple drag and drop example:

EXAMPLE:

<!DOCTYPE HTML>
<html>
<head>
<script>
function allowDrop(ev) {
  ev.preventDefault();
}

function drag(ev) {
  ev.dataTransfer.setData("text", ev.target.id);
}

function drop(ev) {
  ev.preventDefault();
  var data = ev.dataTransfer.getData("text");
  ev.target.appendChild(document.getElementById(data));
}
</script>
</head>
<body>

<div id="div1" ondrop="drop(event)" ondragover="allowDrop(event)"></div>

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

</body>
</html>

Make an Element Draggable

First of all: To make an element draggable, set the draggable attribute to true:

EXAMPLE:

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:

EXAMPLE:

function drag(ev) {
ev.dataTransfer.setData("text", ev.target.id);
}

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:

EXAMPLE:

event.preventDefault()

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):

EXAMPLE:

function drop(ev) {
  ev.preventDefault();
  var data = ev.dataTransfer.getData("text");
  ev.target.appendChild(document.getElementById(data));
}

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() 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