Reject undefined/Null element from array in short getting rid of conditional push

compact.js

//https://triin.net/2010/01/13/Fighting_the_uglyness_of_Array.push()

var buttons = [
  new OpenButton(),
  isPayingCustomer() ? new ExportButton() : null,
  new SaveButton(),
  new DeleteButton()
].compact();


Array.prototype.compact = function() {
  return this.filter(function(x) {
    return x !== null && x !== undefined;
  });
};