칸 아카데미. 재귀를 활용한 거듭제곱(정수일 경우)

power.js

var isEven = function(n) {
    return n % 2 === 0;
};

var isOdd = function(n) {
    return !isEven(n);
};

var power = function(x, n) {
    //println("Computing " + x + " raised to power " + n + ".");
    // base case
    if(n===0){
        return 1;
    }
    // recursive case: n is negative 
    if(n<0){
        return 1/power(x,-n);
    }
    // recursive case: n is odd
    if(isOdd(n)===true){
        return x*power(x,n-1);
    }
    // recursive case: n is even
    if(isEven(n)===true){
        var y = power(x,n/2);
        return y*y;
    }
};


//power(3, -1)