Power of Four.js

/*Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:
Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?*/

/**
 * @param {number} num
 * @return {boolean}
 */
var isPowerOfFour = function(num) {
    if(num <= 0)
        return false
    var power = Math.round(Math.log(num)/Math.log(4))
    return Math.pow(4,power) == num
};