The unit you have just added should have current focus, taking focus away from any previously focused unit.
Units should not just become pointless as the later units are unlocked.
It's a waste of time, deleting units just to add the next unit up.
The game balance is completely wrong. I can spend all my resources and then spam the battle button, since there's literally no risk to doing so (having spent all my resources) this very quickly becomes the fastest way to level. Everything other than combat becomes pointless (in particular clicking the resources, that becomes utterly redundant very quickly).
Clean, straight forward, solid Incremental game. I give four stars.
Could do with a tooltip explaining the exact mechanism for selling things for credits, because I sped read through it.
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The game also gets really laggy.
The fact that you repeatedly document.getElementById instead of casting to a variable (which you can namescape by placing in an object literal) means you're wasting tonnes of cycles on doing stuff repeatedly that should be done once.
That you're doing this inside a while loop strikes me as the problem for performance.
Excellent game. Very well done. Fresh, new perspective on a genre.
I think you have an out by one error on the combat stuff, though, because I will quite often see my current batch of Trimps are no longer taking part in combat but their health is not showing as empty.
 "GrindCraft"){kind=icon}
 "Reactor Incremental"){kind=icon}
 "Galactic Clicker"){kind=icon}
 "Runean idle"){kind=icon}
 "Endless Expansion"){kind=icon}
 "The Vault"){kind=icon}
 "Solar King"){kind=icon}
 "Milestone"){kind=icon}
 "Bloodline Legacy"){kind=icon}
 "SOTW: Conquerors"){kind=icon}
 "Spaceport Command"){kind=icon}
 "Trimps Preview"){kind=icon}