Multiple checkboxes

Hello guys, I have multiple checkboxes they return values and stored into array, but i don't know how to prevent duplicating on the same values within. So when first i click on checkbox 1 stored value 1 in array , and od step 2 when i unchecked the same checkbox and checked again it duplicate the value so it is like : 1 1(duplicate).

Here is the code that I'm using:

$(document).ready(function(){ $('.column-id :checkbox').on('click', function() {

        if ($(this).is(":checked")) {
            var arr = [];
            var pom = $(this).attr("id");
            arr.push(pom);
        }
        /*if($(this).not(":checked")){
            //console.log(arr);
           // var grk = jQuery.inArray( pom , arr );

        }*/


       /* if ($(this).is(":checked")) {
             var dump = $(this).attr("id");
               var arr = [];

               arr.push(dump);
            alert(arr.indexOf(this))x
           // var a = arr.indexOf(this);

            alert(a)*//*
        }*//*else if($(this).not(":checked")){
            var exclude  = $(this).attr("id");

        }*/
        for($i = 0;$i<arr.length;$i++){
            $(".modal-body").append(arr[$i]);
        }
      });
        console.log(arr);

    });

All the best Maja .