countSubstringOccur(['in', 'We are living in a yellow submarine. We don\'t have anything else. Inside the submarine is very tight. So we are drinking all the day. We will move out of it in 5 days.'])
countSubstringOccur(['your', 'No one heard a single word you said. They should have seen it in your eyes. What was going around your head.']);
countSubstringOccur(['but', 'But you were living in another world tryin\' to get your message through.']);

function countSubstringOccur(value) {
    var keyword = value[0].toLowerCase();
    var text = value[1].toLowerCase();
    var matched = new RegExp(keyword, "g");
    var counter = text.match(matched);

    return console.log(counter.length);
}