$(document).ready(function(){
  $('#lol').keypress(function(){
    var data = $('#lol').val().split('n');
    var result = data.filter((word, i, arr) => arr.indexOf(word) === i);
    $('#lol').val(result.join('n'));
    data.unique();
  });
});

(function() {
    "use strict";

    Array.prototype.unique = function unique() {
        var self = this;
        return self.filter(function(a) {
            var that = this;
            // console.log(that);
            if(!that[a]) {
                return that[a] = true;
            } else {
                alert("duplicate");
                return that[a] = false;
            }
        }, {});
    }
})();