Math.abs(number) 

function ComparePosNegVal(n)
{
   var s;
   var v1 = Math.abs(n);
   var v2 = Math.abs(-n);
   if (v1 == v2)
      s = "The absolute values of " + n + " and "
      s += -n + " are identical.";
   return(s);
}