if you need help let me know because im a self-proclaimed keyvalue master

you should use .toString so the user doesn't have to input host with ' '

and maybe a for loop so you don't have to individually write out every single letter and number

valueone.toString() += valuetwo.toString(); maybe

oh wait i think I misinterpreted the question,
do you mean the substrings are causing the error
or the joining is causing the error

hmm, try
if(theSubstring){
doStuff();
}

2 things:
1: in the 'if mouse pressed over online' thing, instead of var Result = "thing", I would recommend Result = "thing" (it would be preferable if it is defined once, it can be defined in or out of the loop, depending on the code stuff) [also I'm pretty sure u can't use getKeyValue on things other than key/value pairs so maybe change Result/the other variables in (s)getKeyValue to a key/value pair?]
2: Only define things once or else it'll break sometimes (I know from personal experience)

Looks cool! I can't wait to see the finished version!

some glitches you might already know about:
you can press space to serve at any time, not just before the game starts
if you drag the player by clicking all the way down, the player gets stuck underneath the barrier and you can't get the player back

Fluffypoopo
wdym balancing