vue自定义指令之面板拖拽的实现

<div v-drag="'refName'"></div>

directives: {
 drag: {
 // 使用bind会有可能没有渲染完成
 inserted: function(el, binding, vnode) {
 const _el = el; //获取当前元素
 const ref = vnode.context.$refs[binding.value]; // 判断基于移动的是哪一个盒子
 const masterNode = ref ? ref : document; // 用于绑定事件
 const masterBody = ref ? ref : document.body; // 用于获取高和宽
 const mgl = _el.offsetLeft;
 const mgt = _el.offsetTop;
 const maxWidth = masterBody.clientWidth;
 const maxHeight = masterBody.clientHeight;
 const elWidth = _el.clientWidth;
 const elHeight = _el.clientHeight;
 let positionX = 0,
 positionY = 0;
 _el.onmousedown = e => {
 //算出鼠标相对元素的位置，加上的值是margin的值
 let disX = e.clientX - _el.offsetLeft + mgl; 
 let disY = e.clientY - _el.offsetTop + mgt;
 masterNode.onmousemove = e => {
 //用鼠标的位置减去鼠标相对元素的位置，得到元素的位置
 let left = e.clientX - disX;
 let top = e.clientY - disY;
 // 绑定的值不能滑出基于盒子的范围
 left < 0 && (left = 0);
 left > (maxWidth - elWidth - mgl) && (left = maxWidth - elWidth - mgl);
 top < 0 && (top = 0);
 top > (maxHeight - elHeight - mgt) && (top = maxHeight - elHeight - mgt);
 //绑定元素位置到positionX和positionY上面
 positionX = top;
 positionY = left;
 
 //移动当前元素
 _el.style.left = left + "px";
 _el.style.top = top + "px";
 };
 // 这里是鼠标超出基于盒子范围之后再松开，会监听不到
 document.onmouseup = e => {
 masterNode.onmousemove = null;
 document.onmouseup = null;
 };
 };
 }
 }
 }