avalonJS里avalon.define = function(id, factory) {? ? var $id = id.$id || id? ? if (!$id) {? ? ? ? log("warning: vm必須指定$id")? ? }? ? if (VMODELS[$id]) {? ? ? ? log("warning: " + $id + " 已經(jīng)存在于avalon.vmodels中")? ? }? ? if (typeof id === "object") {? ? ? ? var model = modelFactory(id)? ? } else {? ? ? ? var scope = {? ? ? ? ? ? $watch: noop? ? ? ? }? ? ? ? factory(scope) //得到所有定義? ? ? ? model = modelFactory(scope) //偷天換日，將scope換為model? ? ? ? stopRepeatAssign = true? ? ? ? factory(model)? ? ? ? stopRepeatAssign = false? ? }? ? model.$id = $id? ? return VMODELS[$id] = model}請問factory這個參數(shù)有啥作用？