Hello guys I have a problem in getting the response from my ajax. If I display it in the console. I can view it. But How do I assign it in a variable?

Here's what I have.
In my PHP code I have this

public function checkPassword($password){



            $username = $this->session->userdata('username');

            $validate = $this->members_model->checkPassword($password,$username);



            echo $validate;



}

In my jquery I have this

$('#existing').on('keyup',function(){



            var id = '<?php echo $this->session->userdata(user_id); ?>';

            var password_url = '<?php echo site_url(member/checkPassword/' +id+ '); ?>';



            $.ajax({

                type: 'POST',

                url: password_url,

                data: '',

                dataType: 'json',

                success: function(response){



                var g = response;

                if(g == 1){

                    $('#existing_info').html('Password is VALID'); //Doesn't display the VALID if the response is 1. Why?

                }else{

                    $('#existing_info').html('Password is INVALID!');

                }



                }



            });



        });