原始的面向过程代码：
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <style> #box { width: 100px; height: 100px; background: blue; position: absolute; } </style> <title>拖拽</title> <script> var oBox=null; var disX=0; var disY=0; window.onload=function(){ oBox=document.getElementById('box'); oBox.onmousedown=fnDown; }; //鼠标按下事件 function fnDown(ev){ var oEvent = ev||event; disX = oEvent.clientX - oBox.offsetLeft; disY = oEvent.clientY - oBox.offsetTop; document.onmousemove = fnMove; document.onmouseup = fnUp; } //鼠标移动事件 function fnMove(ev){ var oEvent=ev||event; oBox.style.left = oEvent.clientX - disX + 'px'; oBox.style.top = oEvent.clientY - disY + 'px'; } //鼠标抬起事件 function fnUp(){ document.onmousemove = null; document.onmouseup = null; } </script> </head> <body> <div></div> </body> </html>
下面是面向对象的代码
drag.js
/** * 拖拽 * @param {Object} id div的id */ function Drag(id){ this.oBox = document.getElementById(id); this.disX = 0; this.disY = 0; var _this = this; this.oBox.onmousedown = function(){ _this.fnDown(); } } //鼠标按下 Drag.prototype.fnDown = function(ev){ var oEvent = ev || event; this.disX = oEvent.clientX - this.oBox.offsetLeft; this.disY = oEvent.clientY - this.oBox.offsetTop; var _this = this; document.onmousemove = function(){ _this.fnMove(); }; document.onmouseup = function(){ _this.fnUp(); }; } //鼠标移动 Drag.prototype.fnMove = function(ev){ var oEvent= ev || event; this.oBox.style.left = oEvent.clientX - this.disX + 'px'; this.oBox.style.top = oEvent.clientY - this.disY + 'px'; } //鼠标抬起 Drag.prototype.fnUp = function(){ document.onmousemove = null; document.onmouseup = null; }
drag.html
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <style> div { position: absolute; } </style> <title>拖拽</title> <script type="text/javascript" src="https://www.jb51.net/js/drag.js" ></script> <script> window.onload = function(){ var drag1 = new Drag("box1"); var drag1 = new Drag("box2"); }; </script> </head> <body> <div></div> <div></div> </body> </html>
此拖拽有一个问题，就是没有控制拖拽出边界的问题。但我们又不想去修改代码，那我们怎么做？学过java的应该都知道可以写一个子类来做一些更加具体的操作，又保留了父类的功能，就是继承。
html
<script type="text/javascript" src="https://www.jb51.net/js/drag.js" ></script> <script type="text/javascript" src="https://www.jb51.net/js/dragLimit.js" ></script> <script> window.onload = function(){ var drag1 = new Drag("box1"); var drag1 = new DragLimit("box2");//蓝色是不会超出边界的 }; </script> <body> <div></div> <div></div> </body>
DragLimit.js：DragLimit继承自Drag，控制了不能出边界
/** * 限制边界的拖拽，继承自Drag * @param {Object} id */ function DragLimit(id){ Drag.call(this, id); } //继承方法 for(var p in Drag.prototype){ DragLimit.prototype[p] = Drag.prototype[p]; } /** * 覆写父类的鼠标移动方法，控制不能移出边界 */ DragLimit.prototype.fnMove = function(ev){ var oEvent= ev || event; var left = oEvent.clientX - this.disX; var top = oEvent.clientY - this.disY; //控制边界 if(left < 0){ left = 0; } else if(left > document.documentElement.clientWidth-this.oBox.offsetWidth){ left = document.documentElement.clientWidth-this.oBox.offsetWidth; } if(top <= 0){ top = 0; } else if(top > document.documentElement.clientHeight-this.oBox.offsetHeight){ top = document.documentElement.clientHeight-this.oBox.offsetHeight; } this.oBox.style.left = left + 'px'; this.oBox.style.top = top + 'px'; }
感兴趣的朋友可以使用在线HTML/CSS/JavaScript代码运行工具：测试上述代码运行效果。
更多关于JavaScript相关内容感兴趣的读者可查看本站专题：《javascript面向对象入门教程》、《JavaScript错误与调试技巧总结》、《JavaScript数据结构与算法技巧总结》、《JavaScript遍历算法与技巧总结》及《JavaScript数学运算用法总结》