All possible unique combination of a given string

combo.js

var combo = (function() {
    var charList;

    function doCombo(buffer, start) {
        for (var i = start; i < charList.length; i++) {
            buffer.push(charList[i]);
            
            console.log(buffer.join(''));

            doCombo(buffer, i + 1);
            buffer.pop();
        }
    }

    return function(str, k) {
        charList = str.split('');
        doCombo([], 0);
    }
})();

combo('abc');