Discern even or odd WITHOUT using the modulo operator

even-odd-without-modulo.js

// Even or Odd
// Determine even or odd WITHOUT the modulo operator
// My aim is to add or subtract two from the input until I reach 0 or 1
// If it concludes on 0 it is even, and if on 1 it is odd
function determineIfEven(num1) {
    switch (!isNaN(num1)) {
        case (num1 == 0):               // If the input is 0 then even
            console.log(true);          // Output boolean true
            break;
        case (num1 == 1):               // If the input is 1 then not even
            console.log(false);         // Output boolean false
            break;
        case (num1 > 1 || num1 < 0):    // If not 0 or 1 enter this case
            if (num1 > 1) {             // If num1 is greater than 1 then subtract 2 from num1
                while (num1 > 1) {      // Use loop to preserve the stack, rather than recusive call
                    num1 -= 2;          // Subtract 2 until num1 is not greater than 1
                }
            } else {                    // If num1 is less than 0 then add 2 to num1
                while (num1 < 0) {      // Loop to preserve stack, rather than recusive call
                    num1 += 2;          // Add 2 until num1 is not less than 0
                }            
            }
            determineIfEven(num1);      // Recall the function with mutated num1 as parameter        
        default:
            break;
    }
}