such that an object literal contains the parameters you want to send and the result is a string you can send as data.
Here is my first try:
function makeData(obj) {
    var data_send = '';
    _.each(obj, function (val, key) {
        data_send += encodeURIComponent(key) + '=' + encodeURIComponent(val) + '&';
    });
    data_send.slice(1,-1);
    return data_send;
}
Is this the correct form for ajax post data?
