javascript - preventDefault() 在拖放中阻止了什么？

Question

例如，这里是来自 w3schools.com 的拖放代码:

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));
}

Answer 1

You must cancel the default action for ondragenter and ondragover in order for ondrop to fire. In the case of a div, the default action is not to drop. This can be contrasted with the case of an input type=text element, where the default action is to drop. In order to allow a drag-and-drop action on a div, you must cancel the default action