OnClientClick="return fucCheckJpgAndGif(form1.File1.value);" --其中File1为上传文件控件

function fucCheckJpgAndGif(strFileName) {     if (strFileName != "") {         var strtype = strFileName.substring(strFileName.length - 4, strFileName.length);         strtype = strtype.toLowerCase();         if ((strtype == ".jpg") || (strtype == ".gif") || (strtype == "jpeg") || (strtype == ".bmp")) {             return true;         }         else {             alert("请上传jpg、gif或者bmp格式的图片，谢谢！");             return false;         }     }     alert("请上传jpg、gif或者bmp格式的图片，谢谢！");/* from http://yige.org/js/ */     return false; }