JSON return string ajax

You need Json stringify. Please look for it on internet

An example :

PHP Code:

$('#send-button').click(function(){
     $.each($('#holder').serializeArray(), function() {
    answer[this.name] = this.value;
    
});
             
var answers = JSON.stringify(answer, null, 2);
      $.ajax({
          url : "<?php echo base_url('your-controller-and-method');?>",
          method: "POST",

etc.