Power sets

powerset.coffee

powerSet = (set) ->
  p = [[]]
  for val in set
    for i in [0...p.length]
      p[p.length] = p[i].concat([val])
  p

powerset.js

var powerSet = function(set) {
  var p = [[]];
  for (var i = 0, il = set.length; i < il; ++i) {
    var val = set[i];
    for (var j = 0, jl = p.length; j < jl; ++j) {
      p[p.length] = p[j].concat([val])
    }
  }
  return p;
};