javascript绘制矩形框_javascript技巧

来源：非凡科技

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

<html> 
<head> 
<title>Rect</title> 
<style type="text/css"> 
</style> 
 
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> 
</head> 
<body> 
 
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"/> 
</body> 
 
//测试代码开始 
//初始化 
Rect.init("main");

document.getElementById('t').onclick = function(){ 
 Rect.container.onmousedown = null; 
}; 
 </ script> 
</html>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]