我有一个调试器日志，是用 JavaScript 为我正在处理的项目编写的。日志基本上是<aside>HTML5 中的一个标签，只在需要时显示。我想尝试一下能够在屏幕上移动日志的想法，因为它可能会重叠某些东西（这对我的项目来说很好）。但是，我似乎无法弄清楚如何使用 HTML5 正确拖放标签，以便将其放置在屏幕上的任何位置（好吧，或在<div>元素内）。
在阅读了 HTML5 的拖放支持后，我对它的工作原理有了基本的了解，但是当涉及允许将 div 放置在任何地方时我不确定从哪里开始（它的 z-index 是一个高值，所以正如我所说，重叠很好）。
有什么建议？
哦，我想尽量避免在这个项目中使用外部库。我试图在纯 JavaScript/HTML5 中做到这一点。
拖放不会移动元素，如果您希望元素在放置时移动，则必须在放置事件中设置元素的新位置。我已经做了一个在 Firefox 和 Chrome 中工作的例子，这里是要点：
function drag_start(event) {
var style = window.getComputedStyle(event.target, null);
event.dataTransfer.setData("text/plain",
(parseInt(style.getPropertyValue("left"),10) - event.clientX) + ',' + (parseInt(style.getPropertyValue("top"),10) - event.clientY));
}
该dragstart事件计算鼠标指针距元素左侧和顶部的偏移量，并将其传递到dataTransfer. 我不担心传递 ID，因为页面上只有一个可拖动元素 - 没有链接或图像 - 如果您的页面上有任何这些内容，那么您将不得不在这里做更多的工作。
function drop(event) {
var offset = event.dataTransfer.getData("text/plain").split(',');
var dm = document.getElementById('dragme');
dm.style.left = (event.clientX + parseInt(offset[0],10)) + 'px';
dm.style.top = (event.clientY + parseInt(offset[1],10)) + 'px';
event.preventDefault();
return false;
}
该drop事件解包偏移量并使用它们相对于鼠标指针定位元素。
该dragover事件只需要preventDefault在任何拖过。同样，如果页面上还有其他可拖动的内容，您可能需要在这里做一些更复杂的事情：
function drag_over(event) {
event.preventDefault();
return false;
}
因此，将其document.body与drop事件一起绑定以捕获所有内容：
var dm = document.getElementById('dragme');
dm.addEventListener('dragstart',drag_start,false);
document.body.addEventListener('dragover',drag_over,false);
document.body.addEventListener('drop',drop,false);
如果你想让它在 IE 中工作，你需要将 转换aside为一个a元素，当然，所有的事件绑定代码都会不同。据我所知，拖放 API 在 Opera 或任何移动浏览器中都不起作用。另外，我知道你说过你不想使用 jQuery，但是跨浏览器事件绑定和操作元素位置是 jQuery 使事情变得容易得多的事情。
感谢您的回答。它在 Chrome 和 Firefox 中运行良好。我调整它以在 IE 中工作。下面是代码。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="generator" content="CoffeeCup HTML Editor (www.coffeecup.com)">
<meta name="dcterms.created" content="Fri, 27 Jun 2014 21:02:23 GMT">
<meta name="description" content="">
<meta name="keywords" content="">
<title></title>
<!--[if IE]>
<script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<style>
li
{
position: absolute;
left: 0;
top: 0; /* set these so Chrome doesn't return 'auto' from getComputedStyle */
width: 200px;
background: rgba(255,255,255,0.66);
border: 2px solid rgba(0,0,0,0.5);
border-radius: 4px; padding: 8px;
}
</style>
<script>
function drag_start(event) {
var style = window.getComputedStyle(event.target, null);
var str = (parseInt(style.getPropertyValue("left")) - event.clientX) + ',' + (parseInt(style.getPropertyValue("top")) - event.clientY) + ',' + event.target.id;
event.dataTransfer.setData("Text", str);
}
function drop(event) {
var offset = event.dataTransfer.getData("Text").split(',');
var dm = document.getElementById(offset[2]);
dm.style.left = (event.clientX + parseInt(offset[0], 10)) + 'px';
dm.style.top = (event.clientY + parseInt(offset[1], 10)) + 'px';
event.preventDefault();
return false;
}
function drag_over(event) {
event.preventDefault();
return false;
}
</script>
</head>
<body ondragover="drag_over(event)" ondrop="drop(event)">
<ul>
<li id="txt1" draggable="true" ondragstart="drag_start(event)"> Drag this text </li><br>
<li id="txt2" draggable="true" ondragstart="drag_start(event)"> Drag me</li>
</ul>
<p>I never am really satisfied that I understand anything; because, understand it well as I may, my comprehension can only be an infinitesimal fraction of all I want to understand about the many connections and relations which occur to me, how the matter in question was first thought of or arrived at, etc., etc.</p>
<p>In almost every computation a great variety of arrangements for the succession of the processes is possible, and various considerations must influence the selections amongst them for the purposes of a calculating engine. One essential object is to choose that arrangement which shall tend to reduce to a minimum the time necessary for completing the calculation.</p>
<p>Many persons who are not conversant with mathematical studies imagine that because the business of [Babbage’s Analytical Engine] is to give its results in numerical notation, the nature of its processes must consequently be arithmetical and numerical, rather than algebraical and analytical. This is an error. The engine can arrange and combine its numerical quantities exactly as if they were letters or any other general symbols; and in fact it might bring out its results in algebraical notation, were provisions made accordingly.</p>
<p>The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis, but it has no power of anticipating any analytical revelations or truths. Its province is to assist us in making available what we are already acquainted with.</p>
</body>
</html>对于多个项目的情况，我调整了一点robertc的好答案。这里的second类名只是为了另一个位置。
<aside draggable="true" class="dragme" data-item="0">One</aside>
<aside draggable="true" class="dragme second" data-item="1">Two</aside>
将 data-item 属性添加到setData函数。
function drag_start(event) {
var style = window.getComputedStyle(event.target, null);
event.dataTransfer.setData("text/plain", (parseInt(style.getPropertyValue("left"), 10) - event.clientX) + ',' + (parseInt(style.getPropertyValue("top"), 10) - event.clientY) + ',' + event.target.getAttribute('data-item'));
}
定位被拖动的元素。
function drop(event) {
var offset = event.dataTransfer.getData("text/plain").split(',');
var dm = document.getElementsByClassName('dragme');
dm[parseInt(offset[2])].style.left = (event.clientX + parseInt(offset[0], 10)) + 'px';
dm[parseInt(offset[2])].style.top = (event.clientY + parseInt(offset[1], 10)) + 'px';
event.preventDefault();
return false;
}
并使用 class 循环遍历所有元素dragme。
var dm = document.getElementsByClassName('dragme');
for (var i = 0; i < dm.length; i++) {
dm[i].addEventListener('dragstart', drag_start, false);
document.body.addEventListener('dragover', drag_over, false);
document.body.addEventListener('drop', drop, false);
}