实现拖拽排序功能，废话少说，上代码

html部分

<ul id="dom">
        <!-- 不要忘记添加拖拽属性 draggable -->
        <li draggable="true">1</li>
        <li draggable="true">2</li>
        <li draggable="true">3</li>
</ul>

js部分

        dragEvent（）
        function dragEvent() {
            let node = document.querySelector("#dom");
            let draging = null;
            //使用事件委托，将li的事件委托给ul
            node.ondragstart = function (event) {
                event.dataTransfer.setData("te", event.target.innerText); //不能使用text，firefox会打开新tab
                draging = event.target;
            }
            node.ondragover = function (event) {
                event.preventDefault();
                let 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") {
                    if (target !== draging) {
                        let targetRect = target.getBoundingClientRect();
                        let dragingRect = draging.getBoundingClientRect();
                        if (target) {
                            if (target.animated) {
                                return;
                            }
                        }
                        if (_index(draging) < _index(target)) {
                            target.parentNode.insertBefore(draging, target.nextSibling);
                        } else {
                            target.parentNode.insertBefore(draging, target);
                        }
                        _animate(dragingRect, draging);
                        _animate(targetRect, target);
                    }
                }
            }
            node.ondrop = () => { }
            //获取元素在父元素中的index
            function _index(el) {
                let index = 0;

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

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

                return index;
            }

            function _animate(prevRect, target) {
                let ms = 300;

                if (ms) {
                    let currentRect = target.getBoundingClientRect();

                    if (prevRect.nodeType === 1) {
                        prevRect = prevRect.getBoundingClientRect();
                    }

                    _css(target, 'transition', 'none');
                    _css(target, 'transform', 'translate3d(' +
                        (prevRect.left - currentRect.left) + 'px,' +
                        (prevRect.top - currentRect.top) + 'px,0)'
                    );

                    target.offsetWidth; // 触发重绘
                    _css(target, 'transition', 'all ' + ms + 'ms');
                    _css(target, 'transform', 'translate3d(0,0,0)');

                    clearTimeout(target.animated);
                    target.animated = setTimeout(function () {
                        _css(target, 'transition', '');
                        _css(target, 'transform', '');
                        target.animated = false;
                    }, ms);
                }
            }
            //给元素添加style
            function _css(el, prop, val) {
                let style = el && el.style;

                if (style) {
                    if (val === void 0) {
                        if (document.defaultView && document.defaultView.getComputedStyle) {
                            val = document.defaultView.getComputedStyle(el, '');
                        } else if (el.currentStyle) {
                            val = el.currentStyle;
                        }

                        return prop === void 0 ? val : val[prop];
                    } else {
                        if (!(prop in style)) {
                            prop = '-webkit-' + prop;
                        }

                        style[prop] = val + (typeof val === 'string' ? '' : 'px');
                    }
                }
            }
        }

效果如下

drag.gif