Permutations

var perm = (function(){
    function perm(xs, ys, o){
        if(ys.length){
            for(var i=0,v;(v=xs+ys.charAt(i)),i<ys.length;i++){
                o[v] = 1;
                perm(v, ys.slice(0,i) + ys.slice(i + 1),o)
            }
        }
    }
    return function(ys){
        var o = {}, a = []
        perm('',ys, o)
        for(var i in o)
            a[a.length] = i;
        return a;
    }
})()

var p = perm('abcdef')