This function returns "true" if the number is power of 2, if not, returns the previous number power of two.

pwer-of-two.js

function checkIfIsPowerOfTwoOrReturnPrevious(number) {
  var previousNumber = number
  number = number | (number >> 1);
  number = number | (number >> 2);
  number = number | (number >> 4);
  number = number | (number >> 8);
  number = number | (number >> 16);
  var result = number - (number >> 1);
  if (result === previousNumber) {
    result = true
  }
  return result;
}

checkIfIsPowerOfTwoOrReturnPrevious(1024) // true is power of 2
checkIfIsPowerOfTwoOrReturnPrevious(46192) // 32768 prev power of 2