doc: added docs for app.replaceModel

docs/API.md

@@ -210,6 +210,14 @@ Register model, view [#Model](#model)  for details.
 
 Unregister model.
 
+### `app.replaceModel(model)`
+
+> Only available after `app.start()` got called
+
+Replace an existing model with a new one, comparing by the namespace. If no one matches, add the new one. 
+
+After called, old `reducers`, `effects`, `subscription` will be replaced with the new ones, while orginal state will be kept, which means it's useful for HMR.
+
 ### `app.router(({ history, app }) => RouterConfig)`
 
 Register router config.
@@ -344,4 +352,4 @@ Store subscriptions in key/value Object. Subscription is used for subscribing da
 
 `({ dispatch, history }, done) => unlistenFunction`
 
-Notice: if we want to unregister a model with `app.unmodel()`, it's subscriptions must return unsubscribe method.
+Notice: if we want to unregister a model with `app.unmodel()` or `app.replaceModel()`, it's subscriptions must return unsubscribe method.

docs/api/README.md

@@ -206,6 +206,14 @@ persistStore(app._store);
 
 取消 model 注册，清理 reducers, effects 和 subscriptions。subscription 如果没有返回 unlisten 函数，使用 `app.unmodel` 会给予警告⚠️。
 
+### `app.replaceModel(model)`
+
+> 只在app.start()之后可用
+
+替换model为新model，清理旧model的reducers, effects 和 subscriptions，但会保留旧的state状态，对于HMR非常有用。subscription 如果没有返回 unlisten 函数，使用 `app.unmodel` 会给予警告⚠️。 
+
+如果原来不存在相同namespace的model，那么执行`app.model`操作
+
 ### `app.router(({ history, app }) => RouterConfig)`
 
 注册路由表。