<!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">
 <head>
 <meta name="DEscription" contect="my code demo" />
 <meta name="Author" contect="Michael@jb51.net" />
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 <title>js check file size @ jb51.net</title>
 </head>
 <body>
  <img id="tempimg" dynsrc="" src="" style="display:none" />
  <input type="file" name="file" id="fileuploade" size="40" />
  <input type="button" name ="check" value="checkfilesize" onclick="checkfile()"/>
 </body>
 <script type="text/javascript">
  var maxsize = 2*1024*1024;//2M
  var errMsg = "上傳的附件文件不能超過2M?。。?;
  var tipMsg = "您的瀏覽器暫不支持計算上傳文件的大小，確保上傳文件不要超過2M，建議使用IE、FireFox、Chrome瀏覽器。";
  var browserCfg = {};
  var ua = window.navigator.userAgent;
  if (ua.indexOf("MSIE")>=1){
   browserCfg.ie = true;
  }else if(ua.indexOf("Firefox")>=1){
   browserCfg.firefox = true;
  }else if(ua.indexOf("Chrome")>=1){
   browserCfg.chrome = true;
  }
  function checkfile(){
   try{
     var obj_file = document.getElementById("fileuploade");
     if(obj_file.value==""){
      alert("請先選擇上傳文件");
      return;
     }
     var filesize = 0;
     if(browserCfg.firefox || browserCfg.chrome ){
      filesize = obj_file.files[0].size;
     }else if(browserCfg.ie){
      var obj_img = document.getElementById('tempimg');
      obj_img.dynsrc=obj_file.value;
      filesize = obj_img.fileSize;
     }else{
      alert(tipMsg);
     return;
     }
     if(filesize==-1){
      alert(tipMsg);
      return;
     }else if(filesize>maxsize){
      alert(errMsg);
      return;
    }else{
     alert("文件大小符合要求");
      return;
    }
   }catch(e){
    alert(e);
   }
  }
 </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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