Transform CamelCase into separated words

decamelize.js

    function decamelize(str, separator){
        separator = typeof separator === 'undefined' ? '_' : separator;

        return str
            .replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
            .replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2')
            .toLowerCase();
    }