PowerSet of a set in 16 lines of JavaScript

PowerSet

function powerSet(s) {   
    if(s.length === 0){
        return [[]];
    }
    
    var headOfList = s.splice(0,1)[0];
    var powerSetOfListTail = powerSet(s);
    var powerSetOfListTailWithHead = powerSetOfListTail.map(function(p) { 
        var cpy = p.slice();
        cpy.push(headOfList);        
        return cpy;
    });
    
    return powerSetOfListTail.concat(powerSetOfListTailWithHead);    
}

powerSet([1,2,3]);