前端js限制上传文件类型及大小（1）

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript">
var isIE = /msie/i.test(navigator.userAgent) && !window.opera;
function fileChange(target,id) {
var fileSize = 0;
var filetypes =[".jpg",".png",".rar",".txt",".zip",".doc",".ppt",".xls",".pdf",".docx",".xlsx"];
var filepath = target.value;
var filemaxsize = 1024*2;//2M
if(filepath){
var isnext = false;
var fileend = filepath.substring(filepath.indexOf("."));
if(filetypes && filetypes.length>0){
for(var i =0; i<filetypes.length;i++){
if(filetypes[i]==fileend){
isnext = true;
break;
}
}
}
if(!isnext){
alert("不接受此文件类型！");
target.value ="";
return false;
}
}else{
return false;
}
if (isIE && !target.files) {
var filePath = target.value;
var fileSystem = new ActiveXObject("Scripting.FileSystemObject");
if(!fileSystem.FileExists(filePath)){
alert("附件不存在，请重新输入！");
return false;
}
var file = fileSystem.GetFile (filePath);
fileSize = file.Size;
} else {
fileSize = target.files[0].size;
}
var size = fileSize / 1024;
if(size>filemaxsize){
alert("附件大小不能大于"+filemaxsize/1024+"M！");
target.value ="";
return false;
}
if(size<=0){
alert("附件大小不能为0M！");
target.value ="";
return false;
}
}
</script>
</head>
<body>
<input type="file" name="contractFileName" style="width: 500px;" onchange="fileChange(this);"/>
</body>
</html>