Actions

firstNumber = 0 , secondNumber = 0;
    function action(firstNumber , secondNumber) {
         switch (field.value) {
                case "+":
                        result = firstNumber + secondNumber;
                    break;
                    case "-":
                        result = firstNumber - secondNumber;
                    break;
                    case "*":
                        result = firstNumber * secondNumber;
                    break;
                    case "/":
                        result = firstNumber / secondNumber;
                    break;
                }
        field.value = result;
    }