Prints combinations of given string

combo_string.js

var combo = (function() {
    var limit = 0;

    function doCombo(charList, buffer, level, start) {
        if (level === limit) {
            console.log(buffer.join(' * '));
            return;
        }

        for (var i = start; i < charList.length; i++) {
            var char = charList[i];

            buffer.push(char);
            doCombo(charList, buffer, level + 1, i + 1);

            buffer.pop();
        }
    }

    return function(str, k) {
        var charList = str.split('');
        var buffer = [];
        var level = 0;
        var start = 0;
        var used = [];
        limit = k;

        doCombo(charList, buffer, level, start);
    }
})();

combo('abcd', 2);