function calculator() {
  var firstNumber = parseInt(document.getElementById("number1").value);
  var secondNumber = parseInt(document.getElementById("number2").value);
  var operator = document.getElementById("op").value;
  var result = document.getElementById("result");
  var total;
  console.log("Isi dari Variable firstNumber: " + firstNumber);
  console.log("Isi dari Variable secondNumber: " + secondNumber);
  console.log("Isi dari Variable operator: " + operator);
  console.log("Isi dari Variable result: " + result);
  console.log("Isi dari Variable total: " + total);
  if (isNaN(firstNumber) || isNaN(secondNumber)) {
    alert("Fill the form with number!");
  } else {
    if (operator == "+") {
      total = firstNumber + secondNumber;
    } else if (operator == "-") {
      total = firstNumber - secondNumber;
    } else if (operator == "x") {
      total = firstNumber * secondNumber;
    } else if (operator == "/") {
      total = firstNumber / secondNumber;
    }
  }
  result.value = total;
}