Generating a powerset

powerset.js

function powerset(alphabet) {
    var p = [[]];
    for (var i=0; i < alphabet.length; i++) {
        // here the value of len is set at the beginning
        for (var j = 0, l = p.length; j < l; j++) {
            p.push(p[j].concat(alphabet[i]));
            // inspector
            console.log(p);
        }
    }
    return p;
}
// test
powerset(['a','b','c']);