ko.subscribeOnce.js

/**
 * knockout observable subscriber that will get triggered only once at most
 * 
 * @param {fn} handler
 * @param {object} [optional] context
 */

ko.observable.fn.subscribeOnce = function( handler, context ) {
  var subscribtion = this.subscribe(function() {
    handler.apply( this, arguments );
    subscribtion.dispose();
  }, context );
}