本文實例講述了JS拖動鼠標畫出方框實現鼠標選區的方法。分享給大家供大家參考。具體如下：
相當實用的一個JS技巧，拖動鼠標可畫出一個方框，可作為一個選區的功能，可以用來畫流程圖，設計草圖什么的，也可以作為上傳頭像時裁切選擇圖片，在頭像裁切中使用廣泛，鼠標在圖片上拖動拉出一個方框，這個方框就代表著選區的功能，目前網頁上已流行的一種操作。主要是依賴于JavaScript代碼來實現。
運行效果如下圖所示：
具體代碼如下：
<!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>鼠標拖動畫矩形</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>希望本文所述對大家的javascript程序設計有所幫助。
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