ScriptedMetricBuilder these's no reduce_params

Why there's reduce_params on ES 2.3. ScriptedMetricBuilder class anymore? How can I set params for reduce_script ?
Anyone please help me !

the reduceScript() method now takes a Script object. You can set the params on that script object in the constructor. The params(Map) method still exists because these params are shared between the init, map and combine script.