javascript 绘制矩形框_javascript技巧

如果不考虑把整个代码封装起来， 大约5分钟里也可以写出类似的效果，为了把整个代码封装成一个对象，稍微借鉴了Pro Javascript Techniques书中的代例子的风格。
Pro Javascript Techniques书中推荐的drag and drop 例子：http://boring.youngpup.net/2001/domdrag

<title>Rect</title> <style type="text/css"> </style> <script type="text/javascript"> var Rect = { //当前正在画的矩形对象 obj: null, //画布 container: null, //初始化函数 init: function(containerId){ Rect.container = document.getElementById(containerId); if(Rect.container){ //鼠标按下时开始画 Rect.container.onmousedown = Rect.start; } else{ alert('You should specify a valid container!'); } }, start: function(e){ var o = Rect.obj = document.createElement('div'); o.style.position = "absolute"; // mouseBeginX，mouseBeginY是辅助变量，记录下鼠标按下时的位置 o.style.left = o.mouseBeginX = Rect.getEvent(e).x; o.style.top = o.mouseBeginY = Rect.getEvent(e).y; o.style.height = 0; o.style.width = 0; o.style.border = "dotted black 1px"; //向o添加一个叉叉，点击叉叉可以删除这个矩形 var deleteLink = document.createElement('a'); deleteLink.href="#"; deleteLink.onclick = function(){ Rect.container.removeChild(this.parentNode); //this.parentNode.style.display = "none"; //alert(this.tagName); } deleteLink.innerText = "x"; o.appendChild(deleteLink); //把当前画出的对象加入到画布中 Rect.container.appendChild(o); //处理onmousemove事件 Rect.container.onmousemove = Rect.move; //处理onmouseup事件 Rect.container.onmouseup = Rect.end; }, move: function(e){ var o = Rect.obj; //dx，dy是鼠标移动的距离 var dx = Rect.getEvent(e).x - o.mouseBeginX; var dy = Rect.getEvent(e).y - o.mouseBeginY; //如果dx，dy <0,说明鼠标朝左上角移动，需要做特别的处理 if(dx<0){ o.style.left = Rect.getEvent(e).x; } if(dy<0){ o.style.top = Rect.getEvent(e).y; } o.style.height = Math.abs(dy); o.style.width = Math.abs(dx); }, end: function(e){ //onmouseup时释放onmousemove，onmouseup事件句柄 Rect.container.onmousemove = null; Rect.container.onmouseup = null; Rect.obj = null; }, //辅助方法，处理IE和FF不同的事件模型 getEvent: function(e){ if (typeof e == 'undefined'){ e = window.event; } //alert(e.x?e.x : e.layerX); if(typeof e.x == 'undefined'){ e.x = e.layerX; } if(typeof e.y == 'undefined'){ e.y = e.layerY; } return e; } }; </script> <div id="main" style="border: solid red 1px; height:90%; width:60%; curssor: default;"></div> 增加一个按钮，可以关闭绘画效果，用来配合测试删除功能 <input type="button" value="停止绘画" id="t"> <script type="text/javascript"> //测试代码开始 //初始化 Rect.init("main"); document.getElementById('t').onclick = function(){ Rect.container.onmousedown = null; }; </script>
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]