Send form data using ajax

Question

I want to send all input in a form with ajax .I have a form like this.

Answer 1

I have written myself a function that converts most of the stuff one may want to send via AJAX to GET of POST query.
Following part of the function might be of interest:

  if(data.tagName!=null&&data.tagName.toUpperCase()=="FORM") {
    //Get all the input elements in form
    var elem = data.elements;
    //Loop through the element array
    for(var i = 0; i < elem.length; i++) {
      //Ignore elements that are not supposed to be sent
      if(elem[i].disabled!=null&&elem[i].disabled!=false||elem[i].type=="button"||elem[i].name==null||(elem[i].type=="checkbox"&&elem[i].checked==false))
        continue; 
      //Add & to any subsequent entries (that means every iteration except the first one) 
      if(data_string.length>0)
        data_string+="&";
      //Get data for selectbox
      if (elem[i].tagName.toUpperCase() == "SELECT")
      {
        data_string += elem[i].name + "=" + encodeURIComponent(elem[i].options[elem[i].selectedIndex].value) ;
      }
      //Get data from checkbox
      else if(elem[i].type=="checkbox")
      {
        data_string += elem[i].name + "="+(elem[i].value==null?"on":elem[i].value);
      }
      //Get data from textfield
      else
      {
        data_string += elem[i].name + (elem[i].value!=""?"=" + encodeURIComponent(elem[i].value):"=");
      }
    }
    return data_string; 
  }

It does not need jQuery since I don't use it. But I'm sure jquery's $.post accepts string as seconf argument.

Here is the whole function, other parts are not commented though. I can't promise there are no bugs in it:

function ajax_create_request_string(data, recursion) {
  var data_string = '';
  //Zpracovani formulare
  if(data.tagName!=null&&data.tagName.toUpperCase()=="FORM") {
    //Get all the input elements in form
    var elem = data.elements;
    //Loop through the element array
    for(var i = 0; i < elem.length; i++) {
      //Ignore elements that are not supposed to be sent
      if(elem[i].disabled!=null&&elem[i].disabled!=false||elem[i].type=="button"||elem[i].name==null||(elem[i].type=="checkbox"&&elem[i].checked==false))
        continue; 
      //Add & to any subsequent entries (that means every iteration except the first one) 
      if(data_string.length>0)
        data_string+="&";
      //Get data for selectbox
      if (elem[i].tagName.toUpperCase() == "SELECT")
      {
        data_string += elem[i].name + "=" + encodeURIComponent(elem[i].options[elem[i].selectedIndex].value) ;
      }
      //Get data from checkbox
      else if(elem[i].type=="checkbox")
      {
        data_string += elem[i].name + "="+(elem[i].value==null?"on":elem[i].value);
      }
      //Get data from textfield
      else
      {
        if(elem[i].className.indexOf("autoempty")!=-1) {
          data_string += elem[i].name+"=";
        }
        else
          data_string += elem[i].name + (elem[i].value!=""?"=" + encodeURIComponent(elem[i].value):"=");
      }
    }
    return data_string; 
  }
  //Loop through array
  if(data instanceof Array) {
    for(var i=0; i