function once(type, func) {
    var that = this;
    wrap.originalListener = func;
    getListeners(that, type).push(wrap);
    return that;

    function wrap() {
      off.call(that, type, wrap);
      func.apply(this, arguments);
    }
  }
Add one-time event listener.

@function EventLite.prototype.once
@param type {string}
@param func {Function}
@returns {EventLite} Self for method chaining