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: Any element can be draggable.
<!DOCTYPE HTML> <html> <head> <style> #div1 { width: 350px; height: 70px; padding: 10px; border: 1px solid #aaaaaa; } </style> <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> <p>Drag the W3Schools image into the rectangle:</p> <div id="div1" ondrop="drop(event)" ondragover="allowDrop(event)"></div> <br> <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:
<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) {
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
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) {
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
<!DOCTYPE HTML>
<html>
<head>
<style>
#div1, #div2 {
float: left;
width: 100px;
height: 35px;
margin: 10px;
padding: 10px;
border: 1px solid black;
}
</style>
<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>
<h2>Drag and Drop</h2>
<p>Drag the image back and forth between the two div elements.</p>
<div id="div1" ondrop="drop(event)" ondragover="allowDrop(event)">
<img src="img_w3slogo.gif" draggable="true" ondragstart="drag(event)" id="drag1" width="88" height="31">
</div>
<div id="div2" ondrop="drop(event)" ondragover="allowDrop(event)"></div>
</body>
</html>