JS验证上传文件类型

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><HTML><HEAD><TITLE> upload </TITLE><META NAME="Generator" CONTENT="EditPlus"><META NAME="Author" CONTENT=""><META NAME="Keywords" CONTENT=""><META NAME="Description" CONTENT=""></HEAD><BODY><FORM ACTION="load.jsp" METHOD="POST" ENCTYPE="mutipart/form-data" name="myform"> 请选择上传文件：<INPUT TYPE="file" NAME="picture"/><INPUT TYPE="button" value="提 交" onclick="check(myform);"/><INPUT TYPE="button" value="取 消" onclick="window.close();"/></FORM></BODY></HTML>

<script language="javascript">function isEmpty(str){ for(var i=0;i<str.length;i++){  if(str.charAt(i)!==" "){    return false;  } } return true;}function check(form){ var fileName = form.picture.value; if(isEmpty(fileName)){    alert("请选择文件名");    form.picture.focus();    return false; } //lastIndexOf如果没有搜索到则返回为-1    if(fileName.lastIndexOf(".")!=-1) {    var fileType = (fileName.substring(fileName.lastIndexOf(".")+1,fileName.length)).toLowerCase();       var suppotFile = new Array();    suppotFile[0] = "gif";    suppotFile[1] = "bmp";    suppotFile[2] = "jpg";    for(var i =0;i<suppotFile.length;i++){       if(suppotFile[i]==fileType){     return true;    }else{   continue;    }  }  alert("不支持文件类型"+fileType);  return false; }else {  alert("文件只支持JIF，BMP，JPG"); }}</script>

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