isPowerOfTwo.js

// 2의 거듭 제곱 확인

function isPowerOfTwo(number) {
    // 1 (2^0) is the smallest power of two.
    if (number < 1) {
        return false;   
    }
  
    // Let's find out if we can divide the number by two
    // many times without remainder.
    let dividedNumber = number;
    while (dividedNumber !== 1) {
        if (dividedNumber % 2 !== 0) {
            // For every case when remainder isn't zero we can say that this number
            // couldn't be a result of power of two.
            return false;
        }
    
        dividedNumber /= 2;
    }
  
    return true;
}


function isPowerOfTwoBitwise(number) {
    // 1 (2^0) is the smallest power of two.
    if (number < 1) {
        return false;
    }
  
    /*
     * Powers of two in binary look like this:
     * 1: 0001
     * 2: 0010
     * 4: 0100
     * 8: 1000
     *
     * Note that there is always exactly 1 bit set. The only exception is with a signed integer.
     * e.g. An 8-bit signed integer with a value of -128 looks like:
     * 10000000
     *
     * So after checking that the number is greater than zero, we can use a clever little bit
     * hack to test that one and only one bit is set.
     */
    return (number & (number - 1)) === 0;
}


function test() {

    console.log(isPowerOfTwoBitwise(1024));
}

test();