File drag and drop
HTML Drag and Drop interfaces enable web applications to drag and drop files on a web page. This document describes how an application can accept one or more files that are dragged from the underlying platform's file manager and dropped on a web page.
The main steps to drag and drop are to define a drop zone (i.e., a target element for the file drop) and to define event handlers for the drop and dragover events. These steps are described below, including example code snippets.
Define the drop zone
The HTML defines the drop zone as a <div>, and an output region (<pre>) to be populated later.
<div id="drop-zone">
<p>Drag one or more files to this <i>drop zone</i>.</p>
</div>
<pre id="output"></pre>
As the target element, it listens to the drop event to process the dropped file.
const dropZone = document.getElementById("drop-zone");
const output = document.getElementById("output");
dropZone.addEventListener("drop", dropHandler);
In order for the drop event to fire, the element must also cancel the dragover event. Here, we cancel the event on window (which would also cancel the event fired on dropZone as it bubbles up), because we also want to listen for the drop event on window to prevent the default browser action of opening the file when it was not dropped into the drop zone.
window.addEventListener("dragover", (e) => {
e.preventDefault();
});
window.addEventListener("drop", (e) => {
e.preventDefault();
});
Lastly, an application may want to style the drop target element to visually indicate the element is a drop zone. In this example, the drop target element uses the following styling:
#drop-zone {
border: 5px solid blue;
width: 200px;
height: 100px;
}
Note:
dragstart and dragend events are not fired when dragging a file into the browser from the OS. To detect when OS files are dragged into the browser, use dragenter and dragleave.
This means that it is not possible to use setDragImage() to apply a custom drag image/cursor overlay when dragging files from the OS — because the drag data store can only be modified in the dragstart event. This also applies to setData().
Process the drop
The drop event is fired when the user drops the file(s). In the following drop handler, the getAsFile() method is used to access each file. This example shows how to write the name of each dragged file to the console. In a real application, an application may want to process a file using the File API.
Note that in this example, any drag item that is not a file is ignored.
function dropHandler(ev) {
// Prevent default behavior (Prevent file from being opened)
ev.preventDefault();
let result = "";
// Use DataTransferItemList interface to access the file(s)
[...ev.dataTransfer.items].forEach((item, i) => {
// If dropped items aren't files, reject them
if (item.kind === "file") {
const file = item.getAsFile();
result += `• file[${i}].name = ${file.name}\n`;
}
});
output.textContent = result;
}