tinymce.full.js
function once(name, callback, prepend) {
        return on(name, callback, prepend, { once: true });
      }
function once(name, callback, prepend) {
        return on(name, callback, prepend, { once: true });
      }
function once ( name , callback , prepend ) { return on ( name , callback , prepend , { once : true } ) ; }
Binds an event listener to a specific event by name
and automatically unbind the event once the callback fires.

@method once
@param {String} name Event name or space separated list of events to bind.
@param {callback} callback Callback to be executed when the event occurs.
@param {Boolean} first Optional flag if the event should be prepended. Use this with care.
@return {Object} Current class instance.
@example
instance.once('event', function(e) {
// Callback logic
});
Binds an event listener to a specific event by name and automatically unbind the event once the callback fires .