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：

/p>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

鼠标拖动画矩形

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}

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);

}

希望本文所述对大家的javascript程序设计有所帮助。