nl_tokens: Returns a wrapper function that ensures the given callback function is only called once . Subsequent calls are ignored unless the first argument is an Error in which case the error is thrown .
pl_tokens: function callOnce ( fn ) { let fulfilled = false ; return function onceWrapper ( err ) { if ( ! fulfilled ) { fulfilled = true ; return fn . apply ( this , arguments ) ; } else if ( err ) { // The callback has already been called, but now an error has occurred // (most likely inside the callback function). So re-throw the error, // so it gets handled further up the call stack throw <mask> ; } } ; }