The easy way

The easiest way is to use the .ajaxStop() event handler:

$(document).ajaxStop(function() {
  // place code to be executed on completion of last outstanding ajax call here
});

The hard way

You can also manually detect if any ajax call is still active:

Create a variable containing number of active Ajax connections:

var activeAjaxConnections = 0;

just before opening new Ajax connection increment that variable

$.ajax({
  beforeSend: function(xhr) {
    activeAjaxConnections++;
  },
  url (...)

in success part check if that variable equals to zero (if so, the last connection has finished)

success: function(html){
  activeAjaxConnections--;
  $('#result_'+rowNum).empty().append(html);
  $('#coda_'+rowNum).removeClass("loading");
  $('#coda_'+rowNum).addClass("loader");
  if (0 == activeAjaxConnections) {
    // this was the last Ajax connection, do the thing
  }
},
error: function(xhr, errDesc, exception) {
  activeAjaxConnections--;
  if (0 == activeAjaxConnections) {
    // this was the last Ajax connection, do the thing
  }
}

As you can see, I’ve added also checking for return with error