underscore.js mixin for set key of nested object

_.replaceKey.coffee

_.mixin
  replaceKey: (obj, key, value) ->
    _obj = _(obj)
    _obj.each (v, k) ->
      if k == key
        obj[k] = value
      else if obj[k] == Object(obj[k])
        replaceKey obj[k], key, value
      return
    _obj

# usage
# obj = {a: 1 , b: [{a: 2}]}
# _.replaceKey(obj, 'a', 3)
#obj-> a: 3 , b: [{a: 3}]}