Jquery Ajax异步上传

<script>
$(function(){
    
    $('#filephoto').change(function(imgFile){
        console.log(imgFile)
        var filextension = imgFile.target.value.substring(imgFile.target.value.lastIndexOf("."), imgFile.target.value.length);
        filextension = filextension.toLowerCase();
        var file = imgFile.target.files[0], fileSize = 0;
        fileSize = file.size / 1024
        if (fileSize > 2048) {
            layer.msg('不能超过2mb')
            return false;
        }
        if ((filextension != '.jpg') && (filextension != '.gif') && (filextension != '.jpeg') && (filextension != '.png') && (filextension != '.bmp')) {
            layer.msg('对不起，系统仅支持标准格式的照片，请您调整格式后重新上传，谢谢!')
            return false;
        }
        var _this = this;
        var fd = new FormData();
        fd.append("filephoto", file);//$_FILES['filephoto']['tmp_name'];
        $.ajax({
            type: 'post',
            url: 'url',
            data:fd,
            processData: false,
            contentType: false,
            dataType: 'json',
        }).done(function (data) {            
            if(data.returnNo == '0000') {
                $("#div_photo").css("background-image","url("+data.user_info.photo+")");
            } else {
                layer.msg(data.returnInfo);
            }
        });
    });
});                
</script>