formdata上传图片

    function chartPicture(objid){   var formdata = new FormData(document.getElementById(objid+"-form"));        var oReq = new XMLHttpRequest();        oReq.open("POST", "url", true);        oReq.onload = function(oEvent) {            if(oReq.status==200){                var data = $.parseJSON(oReq.response);                oReq.send(formdata);    }