Need NPC to trigger iff it's in melee range

[ChaosSlayerZ]

Sorry for hijacking a the tread - I have similar question
Suppose I have npc roaming around the zone.
I want NPC to do something when it passes near a player - like emote.
In the case above, npc already have player target, in my case it can be any player anywhere or multiple of them, so I need npc to continuously check around for valid target.

I was thinking - how does exactly aggro works - isn't npc continuously checking if player is in its range? Can't same principle be used?

Thanks!