本文实例讲述了JS拖动鼠标画出方框实现鼠标选区的方法。分享给大家供大家参考。具体如下：
相当实用的一个JS技巧，拖动鼠标可画出一个方框，可作为一个选区的功能，可以用来画流程图，设计草图什么的，也可以作为上传头像时裁切选择图片，在头像裁切中使用广泛，鼠标在图片上拖动拉出一个方框，这个方框就代表着选区的功能，目前网页上已流行的一种操作。主要是依赖于JavaScript代码来实现。
运行效果如下图所示：
具体代码如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh" lang="zh">
<head>
<title>鼠标拖动画矩形</title>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<style type="text/css">
body,h1,h2,h3,h4,h5,h6,hr,p,blockquote,dl,dt,dd,ul,ol,li,pre,form,fieldset,legend,button,input,textarea,th,td{margin:0;padding:0}
html{color:#000;overflow-y:scoll;overflow:-moz-scrollbars-vertical}
.div{position:absolute; border:1px dashed blue; width:0px; height:0px;left:0px; top:0px; overflow:hidden;}
.retc{position:absolute; border:1px solid #CCCCCC; overflow:hidden; background:#EFEFEF}
</style>
</head>
<body>
</body>
<script language = "javascript">
var wId = "w";
var index = 0;
var startX = 0, startY = 0;
var flag = false;
var retcLeft = "0px", retcTop = "0px", retcHeight = "0px", retcWidth = "0px";
document.onmousedown = function(e){
flag = true;
try{
var evt = window.event || e;
var scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
var scrollLeft = document.body.scrollLeft || document.documentElement.scrollLeft;
startX = evt.clientX + scrollLeft;
startY = evt.clientY + scrollTop;
index++;
var div = document.createElement("div");
div.id = wId + index;
div.className = "div";
div.style.marginLeft = startX + "px";
div.style.marginTop = startY + "px";
document.body.appendChild(div);
}catch(e){
//alert(e);
}
}
document.onmouseup = function(){
try{
document.body.removeChild($(wId + index));
var div = document.createElement("div");
div.className = "retc";
div.style.marginLeft = retcLeft;
div.style.marginTop = retcTop;
div.style.width = retcWidth;
div.style.height = retcHeight;
document.body.appendChild(div);
}catch(e){
//alert(e);
}
flag = false;
}
document.onmousemove = function(e){
if(flag){
try{
var evt = window.event || e;
var scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
var scrollLeft = document.body.scrollLeft || document.documentElement.scrollLeft;
retcLeft = (startX - evt.clientX - scrollLeft > 0 ? evt.clientX + scrollLeft : startX) + "px";
retcTop = (startY - evt.clientY - scrollTop > 0 ? evt.clientY + scrollTop : startY) + "px";
retcHeight = Math.abs(startY - evt.clientY - scrollTop) + "px";
retcWidth = Math.abs(startX - evt.clientX - scrollLeft) + "px";
$(wId + index).style.marginLeft = retcLeft;
$(wId + index).style.marginTop = retcTop;
$(wId + index).style.width = retcWidth;
$(wId + index).style.height = retcHeight;
}catch(e){
//alert(e);
}
}
}
var $ = function(id){
return document.getElementById(id);
}
</script>
</html>
希望本文所述对大家的javascript程序设计有所帮助。
