SOURCE

var node = document.querySelector("#container");
var draging = null;
//使用事件委托，将li的事件委托给ul
node.ondragstart = function(event) {
        //console.log("start");
  			//firefox设置了setData后元素才能拖动！！！！
        event.dataTransfer.setData("te", event.target.innerText); //不能使用text，firefox会打开新tab
        //event.dataTransfer.setData("self", event.target);
        draging = event.target;
    }
node.ondragover = function(event) {
        //console.log("onDrop over");
        event.preventDefault();
        var target = event.target;
  			//因为dragover会发生在ul上，所以要判断是不是li
        if (target.nodeName === "LI"&&target !== draging) {
                if (_index(draging) < _index(target)) {
                    target.parentNode.insertBefore(draging,target.nextSibling);
                } else {
                    target.parentNode.insertBefore(draging, target);
                }
        }
    }
	//获取元素在父元素中的index
  function _index(el) {
        var index = 0;

        if (!el || !el.parentNode) {
            return -1;
        }

        while (el && (el = el.previousElementSibling)) {
            //console.log(el);
            index++;
        }

        return index;
    }

<ul id="container">
        <li class="ele" draggable="true">1</li>
        <li class="ele" draggable="true">2</li>
        <li class="ele" draggable="true">3</li>
        <li class="ele" draggable="true">4</li>
</ul>

ul {
        list-style: none;
        margin: 200px;
    }

    .ele {
        width: 100%;
        height: 40px;
        border: 1px solid #999;
        background: #EA6E59;
        margin-top: 2px;
        border-radius: 10px;
        padding-left: 10px;
        color: white;
        cursor: move;
    }