違ってた、こうですね。

direct.product.coffee

  params =
    alpha: [1,2,3]
    beta:[1,5,7,9,2]
    gamma:[2,3]
  
  set = []
  prods = {}
  prod = 1
  for param, idx in d3.entries(params)
    prods[param.key] = prod
    prod *= param.value.length

  for i in [0..prod - 1]
    set[i] = {}
    for key, val of params
      set[i][key] = val[(0|i / prods[key]) % val.length]
  console.log set

配列の組み合わせをゲットする方法です