}

            @assert(state === "writable");
            @transformStreamDefaultControllerPerformTransform(controller, chunk).@then(() => {
                promiseCapability.@resolve();
            }, (e) => {
                promiseCapability.@reject.@call(@undefined, e);
            });
        }, (e) => {
            promiseCapability.@reject.@call(@undefined, e);
        });

        return promiseCapability.@promise;
    }
    return @transformStreamDefaultControllerPerformTransform(controller, chunk);
})