areValidBounds = function(elem) {
  return (
    elem !== null &&
    typeof elem === 'object' &&
    elem.hasOwnProperty('north') &&
    elem.hasOwnProperty('south') &&
    elem.hasOwnProperty('east') &&
    elem.hasOwnProperty('west')
  );
}
Helper that checks whether an array consists of objects
with lat and lng properties
@param {object} elem the element to check
@returns {boolean} whether or not it's valid