Make new array sorted by number of "a"

Implement function moreAFirst of one argument arr which contains array of strings. Function should return new array with strings which have more symbols "a" going first.

console.log(moreAFirst(['a', 'baa', 'zaaa']))
console.log(moreAFirst(['Guatemala', 'Costa Rica', 'Anguilla', 'North Korea', 'Canada']))