This feature is well established and works across many devices and browser versions. It’s been available across browsers since November 2016.
The read-only length property of the DataTransferItemList interface returns the number of items currently in the drag item list.
The number of drag data items in the list, or 0 if the list is empty or disabled. The drag item list is considered to be disabled if the item list's DataTransfer object is not associated with a drag data store.
This example shows the use of the length property.
<div>
<p id="source" draggable="true">
Select this element, drag it to the Drop Zone and then release the selection
to move the element.
</p>
</div>
<div id="target">Drop Zone</div>
div {
margin: 0em;
padding: 2em;
}
#source {
color: blue;
border: 1px solid black;
}
#target {
border: 1px solid black;
}
const source = document.getElementById("source");
const target = document.getElementById("target");
source.addEventListener("dragstart", (ev) => {
console.log("dragStart");
// Add this element's id to the drag payload so the drop handler will
// know which element to add to its tree
const dataList = ev.dataTransfer.items;
dataList.add(ev.target.id, "text/plain");
// Add some other items to the drag payload
dataList.add("<p>Paragraph…</p>", "text/html");
dataList.add("http://www.example.org", "text/uri-list");
});
source.addEventListener("dragend", (ev) => {
console.log("dragEnd");
const dataList = ev.dataTransfer.items;
// Clear any remaining drag data
dataList.clear();
});
target.addEventListener("drop", (ev) => {
console.log("Drop");
ev.preventDefault();
const data = ev.dataTransfer.items;
// Loop through the dropped items and log their data
for (let i = 0; i < data.length; i++) {
if (data[i].kind === "string" && data[i].type.match("^text/plain")) {
// This item is the target node
data[i].getAsString((s) => {
ev.target.appendChild(document.getElementById(s));
});
} else if (data[i].kind === "string" && data[i].type.match("^text/html")) {
// Drag data item is HTML
data[i].getAsString((s) => {
console.log(`… Drop: HTML = ${s}`);
});
} else if (
data[i].kind === "string" &&
data[i].type.match("^text/uri-list")
) {
// Drag data item is URI
data[i].getAsString((s) => {
console.log(`… Drop: URI = ${s}`);
});
}
}
});
target.addEventListener("dragover", (ev) => {
console.log("dragOver");
ev.preventDefault();
// Set the dropEffect to move
ev.dataTransfer.dropEffect = "move";
});
| Specification |
|---|
| HTML> # dom-datatransferitemlist-length-dev> |
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | WebView on iOS | |
length |
13 | 12 | 50 | 12 | 6 | 18 | 50 | ≤14 | 6 | 1.0 | 4.4 | 6 |
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https://developer.mozilla.org/en-US/docs/Web/API/DataTransferItemList/length