nl_tokens: On success check whether the target object is indeed sealed .
pl_tokens: function ( ) { var trap = this . getTrap ( "seal" ) ; if ( trap === undefined ) { // default forwarding behavior return Reflect . seal ( this . target ) ; } var success = trap . call ( this . handler , this . target ) ; success = ! ! <mask> ; // coerce to Boolean if ( success ) { if ( ! Object_isSealed ( this . target ) ) { throw new TypeError ( "can't report non-sealed object as sealed: " + this . target ) ; } } return success ; }