use with .sort() on an array of JSON objects.

comparatorWithPrimer.js

var sort_by = function(field, reverse, primer){

   reverse = (reverse) ? -1 : 1;

   return function(a,b){

       a = a[field];
       b = b[field];

       if (typeof(primer) != 'undefined'){
           a = primer(a);
           b = primer(b);
       }

       if (a<b) return reverse * -1;
       if (a>b) return reverse * 1;
       return 0;

   }
}