<script type="text/javascript">
var n1=10;
var n2=20;
var n = n1++; //n1 = 11 n1++ = 10
console.log('n='+n); // 10
console.log('n1='+n1); //11
n = ++n1 //n1 = 12 ++n1 =12
console.log('n='+n); //12
console.log('n1='+n1); //12
n = n2--;// n2=19 n2--=20
console.log('n='+n); //20
console.log('n2='+n2); //19
n = --n2; //n2=18 --n2 = 18
console.log('n='+n); //18
console.log('n2='+n2); //18
</script>