F-35's internal weapon bays offer the ability to reduce it's combat-config RCS level. But that internal payload is pathetically small. In a multi-mission scenario, a load of 2 AAMs and 2 JDAMs is what you'd as call totally inadequate.
With the kind of missiles USAF F-35s carry (AIM-120D), you really don't have an effective A2A fighter unless you assume that;
1) The enemy is totally oblivious to your presence.
2) The enemy has no idea that he has been seen, locked & fired upon.
3) Even if he realizes he's being attacked, he is incapable of evading or spoofing the threat.
Even if all the above criteria is checked, it still doesn't give you a 100% probability of hit (pH), let alone a 100% probability of kill (pK).
The most plausible outcome of an A2A engagement between F-35 and a capable fighter from a well-trained air force, is that the JSF exhausts it's internal payload and has to RTB without having taken down any enemy planes. In a bad turn for the JSF, if the enemy plane has greater performance threshold (like most Flankers and J-11s), they will kill the F-35 on it's way back.
Being slow, unable to supercruise and not very agile...the F35 will not only be incapable of effectively escaping a Russian/Chinese threat, but will also present a relatively huge IR signature from the rear, allowing a passive search and IR-guided kill.