https://repl.it/BarQ/1 created by Gereltuya

BarQ-1.js

var totthree=0; 
var totfive=0;
var a = 3983;
var dtotal=0;

for (var b=3; b<990; b++) {

if (b%3===0) {
totthree=totthree+b; 
 
}
}

for (var c=5; c<990; c++) {
    if (c%5===0) {
    totfive=totfive+c;

    
    }
}

for  (var d=15; d<990; d++) 
{   if (d%15===0) {
dtotal=dtotal+d;

}

}
console.log((a+totthree+totfive)-dtotal);

BarQ-1_console_dump.txt

Native Browser JavaScript
>>> 232178

in this example, the problem were solved only contemplating till 990 and the rest were added manually (993; 995, 996, 999) and the result is 3983. In this example it is ( var a =3983).

1. Loop b only counting multiples of 3 starting from 3 to 990 and sum result is named "totthree".
2. Loop c only counting multiples of 5 starting from 5 to 990 and sum result is named to be "totfive".
3. Loop d has taken care of duplication for the chance how many times 15 was counted twice starting from 15 to 990. and the sum result is named to dtotal would be considered as deduction to remove duplicated counts.

The total of the loops results came out to be 232178.