Got it. I used more things from w3schools to make a not-so-noob-as-before script
I tested my code and I think it's fully functionable, but feel free to test it for yourself and search for bugs ^^
<script language="javascript" type="text/javascript">
var Credits=document.getElementById('credits_real_value').innerHTML;
var Predits=document.getElementById('credits_promo_value').innerHTML;
var IntPr=Predits.slice(-3);
if(parseInt(Credits) == 0 && parseInt(IntPr) < 500 && Predits.slice(0,-4) == "")
{
document.write("Enter HTML");
}
else
{
document.write("Doesn't work!");
}
</script>
Thank you, Don, I wouldn't make it without you ^^