JavaScript implements the function of clicking the left mouse button for area selection-JS Tutorial-php.cn

JavaScript implements the function of clicking the left mouse button for area selection

巴扎黑

Release： 2017-09-14 11:58:01

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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：

&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
&lt;html xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh" lang="zh">
&lt;head>
&lt;title>鼠标拖动画矩形&lt;/title>
&lt;meta http-equiv="content-type" content="text/html;charset=utf-8">
&lt;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}
.p{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}
&lt;/style>
&lt;/head>
&lt;body> 
&lt;/body>
&lt;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 p = document.createElement("p");
   p.id = wId + index;
   p.className = "p";
   p.style.marginLeft = startX + "px";
   p.style.marginTop = startY + "px";
   document.body.appendChild(p);
  }catch(e){
  //alert(e);
  }
 }
 document.onmouseup = function(){
  try{
   document.body.removeChild($(wId + index));
   var p = document.createElement("p");
   p.className = "retc";
   p.style.marginLeft = retcLeft;
   p.style.marginTop = retcTop;
   p.style.width = retcWidth;
   p.style.height = retcHeight;
   document.body.appendChild(p);
  }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);
 }
&lt;/script>
&lt;/html>

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