file upload lib prototyping

upload.js

function upload(opt) {
    opt = $.extend({
        method:'POST',
        url:'',
        data:{},
        onprogress:function() {},
        onload:function(e, file) {},
        onsuccess:function(e, file) {},
        onerror:function(e, file) {}
    }, opt);

    var xhr = new XMLHttpRequest();
    xhr.open(opt.method, opt.url);

    // native Form Data 세팅
    var form = new FormData();
    for ( var k in opt.data) form.append(k, opt.data[k]);

    xhr.upload.onprogress = opt.onprogress;
    xhr.upload.onload = function(e) {
        opt.onload.apply(null, [e, opt.data.file]);
    };
    xhr.onreadystatechange = function (e) {
        if (e.currentTarget.readyState == 4) {
            if (e.currentTarget.status == 200) opt.onsuccess.apply(null, [e.currentTarget, opt.data.file]);
            else opt.onerror.apply(null, [e.currentTarget, opt.data.file]);
        }
    };
    xhr.send(form);
    return xhr;
}