js判断上传文件的类型和大小

 //检测文件大小和类型
 function fileChange(target){
 //检测上传文件的类型
 if(!(/(?:jpg|gif|png|jpeg)$/i.test(target.value))) {
 alert("只允许上传jpg|gif|png|jpeg格式的图片");
 if(window.ActiveXObject) {//for IE
 target.select();//select the file ,and clear selection
 document.selection.clear();
 } else if(window.opera) {//for opera
 target.type="text";target.type="file";
 } else target.value="";//for FF,Chrome,Safari
 return;
 } else {
 return; //alert("ok");//or you can do nothing here.
 }

 //检测上传文件的大小
 var isIE = /msie/i.test(navigator.userAgent) && !window.opera;
 var fileSize = 0;
 if (isIE && !target.files){
 var filePath = target.value;
 var fileSystem = new ActiveXObject("Scripting.FileSystemObject");
 var file = fileSystem.GetFile (filePath);
 fileSize = file.Size;
 } else {
 fileSize = target.files[0].size;
 }
 var size = fileSize / 1024;
 if(size>(500)){
 alert("文件大小不能超过500KB");
 if(window.ActiveXObject) {//for IE
 target.select();//select the file ,and clear selection
 document.selection.clear();
 } else if(window.opera) {//for opera
 target.type="text";target.type="file";
 } else {
 target.value="";//for FF,Chrome,Safari
 }
 return;
 }else{
 return;
 }
 }