formdata的使用方法

function upload_single_file(value){
    if(value==‘‘){
        layer.msg(‘请添加文件‘,{time:1500})
    }else{
        var formData = new FormData();
        var data = document.getElementById("file").files;
        for (var i = 0; i < data.length; i++) {
            formData.append(‘files[]‘,data[i]);
        };
        $.ajax({
            type : "POST",
            url : "sub_act.php?act=upload_file",
            cache: false,
            data: formData,
            processData: false,
            contentType: false,
            dataType:‘json‘,
            success:function(data){
                if(data.state==‘success‘){
                    var oli=‘‘;
                    if(data.res){
                        for(var i=0;i<data.res.length;i++){
                            oli+="<li><p><a class=‘hr‘ id=‘attachmentDel"+i+"‘ href=‘"+data.res[i].attachment+"‘>"+data.res[i].rel_attachment+"</a></p><a href=‘javascript:;‘ onclick=‘delelteUpFile(\""+data.res[i].attachment+"\",\"attachmentDel"+i+"\")‘>删除</a></li>"
                        }
                        if(document.getElementById(‘upfile_list‘).getElementsByTagName(‘p‘)[0].innerHTML==‘无数据...‘){
                            document.getElementById(‘upfile_list‘).innerHTML=‘‘;
                        }
                        $(‘#upfile_list‘).append(oli);
                    }
                }
            }
        })
    }
}