// The following will change the color of each paragraph to red, just once
// for the "changecolor" key.
$('p').once('changecolor').css('color', 'red');

// .once() will return a set of elements that yet to have the once ID
// associated with them. You can return to the original collection set by
// using .end().
$('p')
  .once("changecolorblue")
    .css("color", "blue")
  .end()
  .css("color", "red");

// To execute a function on the once set, you can use jQuery's each().
$('div.calendar').once().each(function() {
  // Since there is no once ID provided here, the key will be "once".
});