function decimalToOctal(num) {
  var oct = 0,c=0;
  while (num > 0) {
  var r=num%8;
  oct=oct+(r*Math.pow(10,c++));
  num =Math.floor(num/ 8); // basically /= 8 without remainder if any
  }
  console.log("The decimal in octal is " + oct);
}

 decimalToOctal(2);
 decimalToOctal(8);
 decimalToOctal(65);
 decimalToOctal(216);
 decimalToOctal(512);