You have multiple problems in this expression:
var result = Math.max(
Math.min(
Math.round(
(
100 - Math.sqrt(moon_size) * Math.sqrt((deathstar / (220 * Math.max(1, Math.pow(0.90, moonBase))))),
1
),
100),
0
)
);
In your Math.round you have:
(
100 - Math.sqrt(moon_size) * Math.sqrt((deathstar / (220 * Math.max(1, Math.pow(0.90, moonBase))))),
1
)
Which is ( … /* that long expression * / … , 1) do to the comma operator this evaluates always to 1. So this is essential Math.round(1, 100)
So your code does this:
var result = Math.max(
Math.min(
Math.round(1, 100),
0
)
);
The second argument of round is ignored so it is Math.round(1).
And so the remaining code is: Math.max( Math.min(1, 0) ), which is always 0.
You should move at least 100 - Math.sqrt(moon_size) * Math.sqrt((deathstar / (220 * Math.max(1, Math.pow(0.90, moonBase))))) out of your expression and save it in a variable. And then us that variable in your round, min, max expression.
That way you can see if you have the correct braces and parameters.
So fixing those braces results into this:
function destroyMoon() {
var deathstar = $('#deathstar').val();
var moonBase = $('#moonBase').val();
var moonSize = $('#moonSize').val();
var result = Math.max(
Math.min(
Math.round(
100 - Math.sqrt(moonSize) * Math.sqrt((deathstar / (220 * Math.max(1, Math.pow(0.90, moonBase)))))
),
100),
0
)
;
$('#moon_destr').text(result);
}<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table class="list listOfOthers hard-table">
<tr>
<td>Check your moon destroy %
<td>
</tr>
<tr>
<td>Moon base level<input type="text" size="10" value="0" name="moonBase" id="moonBase" onkeyup="destroyMoon();"></td>
<td>Deathstars: <input type="text" size="10" value="0" name="deathstar" id="deathstar" onkeyup="destroyMoon();"></td>
<td>Moon size <input type="text" size="10" value="0" name="moonSize" id="moonSize" onkeyup="destroyMoon();"></td>
<td>Moon destroy chance
<div class="text" id="moon_destr"> 0</div>
</td>
</tr>
</table>