set an error handler for jquery datatables ajax call

Use the Ajax error function to log errors:

$('#table').DataTable({
    ajax: {
        dataType: "JSON",  
        type: "POST",
        url: url,
        data: [],
        async: true,
        error: function (xhr, error, code) {
            console.log(xhr, code);
        }
    },
});

I am using Datatables 1.10.19 + Bootstrap and most of the solutions provided (including the accepted one above) did not work. However, I managed to capture the error as follows:

 "ajax" : {
    "datatype" : "json",
    "contentType" : "application/json",
    "method" : "GET",
    "url" : $url,
    "data" : { x : y },
    "dataSrc": function (data) {
      if (data.result == "OK"){
        return data.yourObj;
      }else{
        // hide processing or any loading modal here
        // display error on page or something
        console.log("Error: " + parseResultData(data.resultData));
        data.yourObj = [] //since datatables will be checking for the object as array
        return data.yourObj;
      }                           
    } 
  }

New error event handling has been added in Datatables v1.10.5 (released 10th February 2015).

$.fn.dataTable.ext.errMode = function ( settings, helpPage, message ) { 
    console.log(message);
};

See docs here:
https://datatables.net/reference/event/error
https://cdn.datatables.net/1.10.5/

Use the event as a custom error handler:

$(document).ready(function () {
    $('#myTable').on('error.dt', function (e, settings, techNote, message) {
        console.log('An error has been reported by DataTables: ', message);
    }).DataTable({
        "displayLength": 15,
        "ajax": {
          ....