code: function( type, handler ) {
  
        if( handler === void 0 || handler === null )
          throw new Error( 'Missing argument "handler"' )
  
        if( typeof handler !== 'function' && typeof handler.handleEvent !== 'function' )
          throw new TypeError( 'Handler must be a function.' )
  
        function wrapper() {
          this.removeListener( type, wrapper )
          typeof handler !== 'function'
            ? handler.handleEvent.apply( handler, arguments )
            : handler.apply( this, arguments )
        }
  
        this._events[ type ] ?
          this._events[ type ].push( wrapper ) :
          this._events[ type ] = [ wrapper ]
  
        return this
  
      }
docs: Adds a one time listener for the specified event
  @param  {String}   type
  @param  {Function} handler
  @return {Emitter}