Get all possible combinations of a pattern (? is replacable by an alphabet)

Pattern combination

function pattern(str, alphabet) {
    alphabet = alphabet || ["0", "1"];
    var chars = str.split("");
    var result = [];
    chars.forEach(function(char) {
        if (result.length == 0) {
            result = [""];
        }
        var newResult = [];
        result.forEach(function(item){
            if (char === '?') {
                alphabet.forEach(function(letter) {
                    newResult.push(item+letter);
                });
            } else {
                newResult.push(item+char);
            }
        });
        result = newResult;
    });
    return result;
}
pattern("01?01??");
pattern("?010?");
pattern("???",["a","b","c"]);