The DataTransfer.effectAllowed property specifies the effect that is allowed for a drag operation. The copy operation is used to indicate that the data being dragged will be copied from its present location to the drop location. The move operation is used to indicate that the data being dragged will be moved, and the link operation is used to indicate that some form of relationship or connection will be created between the source and drop locations.
This property should be set in the dragstart event to set the desired drag effect for the drag source. Within the dragenter and dragover event handlers, this property will be set to whatever value was assigned during the dragstart event, thus effectAllowed may be used to determine which effect is permitted.
Assigning a value to effectAllowed in events other than dragstart has no effect.
A DOMString representing the drag operation that is allowed. The possible values are:
-
none
-
The item may not be dropped.
-
copy
-
A copy of the source item may be made at the new location.
-
copyLink
-
A copy or link operation is permitted.
-
copyMove
-
A copy or move operation is permitted.
-
link
-
A link may be established to the source at the new location.
-
linkMove
-
A link or move operation is permitted.
-
move
-
An item may be moved to a new location.
-
all
-
All operations are permitted.
-
uninitialized
-
The default value when the effect has not been set, equivalent to all.
Assigning any other value to effectAllowed has no effect and the old value is retained.
Internet Explorer will change the value to be lowercased; thus, linkMove will become linkmove, and so on.
This example shows the use of the effectAllowed and dropEffect properties.
<!DOCTYPE html>
<html lang=en>
<title>Examples of DataTransfer.{dropEffect,effectAllowed} properties</title>
<meta content="width=device-width">
<style>
div {
margin: 0em;
padding: 2em;
}
#source {
color: blue;
border: 1px solid black;
}
#target {
border: 1px solid black;
}
</style>
<script>
function dragstart_handler(ev) {
console.log("dragStart: dropEffect = " + ev.dataTransfer.dropEffect + " ; effectAllowed = " + ev.dataTransfer.effectAllowed);
ev.dataTransfer.setData("text", ev.target.id);
ev.dataTransfer.effectAllowed = "move";
}
function drop_handler(ev) {
console.log("drop: dropEffect = " + ev.dataTransfer.dropEffect + " ; effectAllowed = " + ev.dataTransfer.effectAllowed);
ev.preventDefault();
var data = ev.dataTransfer.getData("text");
ev.target.appendChild(document.getElementById(data));
}
function dragover_handler(ev) {
console.log("dragOver: dropEffect = " + ev.dataTransfer.dropEffect + " ; effectAllowed = " + ev.dataTransfer.effectAllowed);
ev.preventDefault();
ev.dataTransfer.dropEffect = "move"
}
</script>
<body>
<h1>Examples <code>DataTransfer</code>.{<code>dropEffect</code>, <code>effectAllowed</code>} properties</h1>
<div>
<p id="source" ondragstart="dragstart_handler(event);" 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" ondrop="drop_handler(event);" ondragover="dragover_handler(event);">Drop Zone</div>
</body>
</html>
