How do I solve this function in Javascript?

// 1) howSwedish

// ABBA is a band, they have many songs including Dancing Queen, and

// Fernando. ABBA is actually a Swedish band, so if we wanted to find

// out howSwedish a String is, we could simply find out how many times

// the String contains the substring "abba". We want to look for this

// substring in a case insensitive manner. So "abba" counts, and so

// does "aBbA". We also want to check for overlapping abba's such as

// in the String "abbAbba" that contains "abba" twice.

// howSwedish("AbBa a b b a") returns 1

// howSwedish("abbabba!") returns 2

function howSwedish(str) {

// TODO: this method

// Use str.length()

// Use + for concatenation

// Use var to declare variables

return 0;

}

// The following asserts will fail until howSwedish is fixed

// console.assert ( 0 == howSwedish ( 'no' ) );

// console.assert ( 1 == howSwedish ( 'axxc AbBa Xx' ) );